SEOUL, South Korea (AP) — South Korea’s military fired warning shots after North Korean soldiers crossed the rivals’ tense border on Tuesday, South Korean officials said, the first known border intrusion by North Korea in nearly a year.

Violent confrontations and bloodshed have occasionally happened at the Koreas’ heavily fortified border, called the Demilitarized Zone. But Tuesday’s incident won’t likely escalate, as it didn’t cause any casualties on either side and North Korea hasn’t returned fire.

About 10 North Korean soldiers — some carrying weapons — violated the military demarcation line at the eastern section of the DMZ at 5 p.m. They returned to North Korea after South Korea broadcast warnings and fired warning shots, South Korea’s Joint Chiefs of Staff said in a statement.

South Korea’s military said it is closely monitoring North Korean activities. It said North Korea didn’t return fire.

In June last year, North Korean troops violated the border three times, prompting South Korea to fire warning shots. The incidents occurred when the Koreas were embroiled in Cold War-style campaigns like balloon launches and propaganda broadcasts, but they didn’t develop into a major source of tensions.

South Korea’s military assessed at the time that the North Korean soldiers didn’t deliberately commit the border intrusion and the site was a wooded area where military demarcation line signs weren’t clearly visible. Observers said the North Korean soldiers might have accidently crossed the border while adding anti-tank barriers, planting mines or engaging in other works to boost border defenses.

The motive for Tuesday’s border crossing by North Korean soldiers wasn’t immediately clear.

South Korea’s military said in late March that North Korea was resuming front-line works such as reinforcing barbed wire fences. South Korean media, citing the military, reported that North Korean soldiers might have unintentionally intruded into South Korea’s territory on Tuesday during a patrol mission ahead of unspecified front-line works.

In October, North Korea said it would build defense structures at the border to cope with “confrontational hysteria” by South Korean and U.S. forces. That was seen as an effort to beef up its front-line security posture and prevent its soldiers and citizens from defecting to South Korea.

The 248-kilometer (155-mile) -long, 4-kilometer (2.5-mile) -wide DMZ is one of the world’s most heavily armed borders. An estimated 2 million mines are peppered inside and near the border, which is also guarded by barbed wire fences, tank traps and combat troops on both sides. It’s a legacy of the 1950-53 Korean War, which ended with an armistice, not a peace treaty.

Animosities between the Koreas are running high now as North Korean leader Kim Jong Un continues to flaunt his military nuclear capabilities and align with Russia over President Vladimir Putin’s war on Ukraine. Kim is also ignoring calls by Seoul and Washington to resume denuclearization negotiations.

Since his Jan. 20 inauguration, U.S. President Donald Trump has said he would reach out to Kim again to revive diplomacy. North Korea has not responded to Trump’s remarks and says U.S. hostilities against it have deepened since Trump’s inauguration. Experts say Kim could eventually return to talks with Trump, hoping that his advancing nuclear program would help North Korea win greater U.S. concessions.

South Korea, meanwhile, is experiencing a leadership vacuum after the ouster of President Yoon Suk Yeol last week over his ill-fated imposition of martial law. Yoon’s push to expand military drills with the U.S. had infuriated North Korea. __

Associated Press writer Kim Tong-hyung contributed to this report.

SEOUL, South Korea (AP) — North Korean leader Kim Jong Un vowed to implement the “toughest” anti-U.S. policy, state media reported Sunday, less than a month before Donald Trump takes office as U.S. president.

Trump’s return to the White House raises prospects for high-profile diplomacy with North Korea. During his first term, Trump met Kim three times for talks on the North’s nuclear program. Many experts however say a quick resumption of Kim-Trump summitry is unlikely as Trump would first focus on conflicts in Ukraine and the Middle East. North Korea’s support for Russia’s war against Ukraine also poses a challenge to efforts to revive diplomacy, experts say.

During a five-day plenary meeting of the ruling Workers’ Party that ended Friday, Kim called the U.S. “the most reactionary state that regards anti-communism as its invariable state policy.” Kim said that the U.S.-South Korea-Japan security partnership is expanding into “a nuclear military bloc for aggression.”

“This reality clearly shows to which direction we should advance and what we should do and how,” Kim said, according to the official Korean Central News Agency.

It said Kim’s speech “clarified the strategy for the toughest anti-U.S. counteraction to be launched aggressively” by North Korea for its long-term national interests and security.

KCNA didn’t elaborate on the anti-U.S. strategy. But it said Kim set forth tasks to bolster military capability through defense technology advancements and stressed the need to improve the mental toughness of North Korean soldiers.

The previous meetings between Trump and Kim had not only put an end to their exchanges of fiery rhetoric and threats of destruction, but they developed personal connections. Trump once famously said he and Kim “fell in love.” But their talks eventually collapsed in 2019, as they wrangled over U.S.-led sanctions on the North.

North Korea has since sharply increased the pace of its weapons testing activities to build more reliable nuclear missiles targeting the U.S. and its allies. The U.S. and South Korea have responded by expanding their military bilateral drills and also trilateral ones involving Japan, drawing strong rebukes from the North, which views such U.S.-led exercises as invasion rehearsals.

Further complicating efforts to convince North Korea to abandon its nuclear weapons in return for economic and political benefits is its deepening military cooperation with Russia.

According to U.S., Ukrainian and South Korean assessments, North Korea has sent more than 10,000 troops and conventional weapons systems to support Moscow’s war against Ukraine. There are concerns that Russia could give North Korea advanced weapons technology in return, including help to build more powerful nuclear missiles.

Ukrainian President Volodymyr Zelenskyy said last week that 3,000 North Korean troops have been killed and wounded in the fighting in Russia’s Kursk region. It was the first significant estimate by Ukraine of North Korean casualties since the North Korean troop deployment to Russia began in October.

Russia and China, locked in separate disputes with the U.S., have repeatedly blocked U.S.-led pushes to levy more U.N. sanctions on North Korea despite its repeated missile tests in defiance of U.N. Security Council resolutions.

Last month, Kim said that his past negotiations with the United States only confirmed Washington’s “unchangeable” hostility toward his country and described his nuclear buildup as the only way to counter external threats.

South Korea was engulfed in six hours of chaos on Tuesday night after the nation’s president, Yoon Suk Yeol, declared “emergency martial law” for the first time in more than 40 years. The decree prompted an immediate outcry, and Yoon was forced to lift the order after the country’s National Assembly unanimously voted to overturn it.

So what happened, and what’s next?

Yoon won South Korea’s presidency in a close election in 2022, but has become deeply unpopular amid efforts to target news organizations and clamp down on dissent. His party, the People Power Party, was handed a sweeping defeat in April, which gave the opposition party a large majority that has stymied his efforts to lead.

Yoon made the decree in a televised address at 11 p.m. on Tuesday night, saying he was doing so to target broad claims of “anti-state” activities while accusing members of South Korea’s main opposition party of working with North Korea. Army Gen. Park An-Su, who was appointed as martial law commander, said that designation barred any political activity or demonstration, and all news media would be placed under “the control of martial law command.”

Martial law was last imposed in South Korea in 1980 before the country became a democracy. At the time, special forces cracked down on pro-democracy activists in a violent spree that killed about 200 people.

Many lawmakers in South Korea’s National Assembly quickly convened for an emergency session to respond to the decree, and less than three hours later all 190 in attendance voted unanimously to revoke the order.

Lee Jae-myung, the leader of the opposition party, urged citizens to convene at Parliament to voice their discontent.

“There is no reason to declare martial law. We cannot let the military rule this country,” Lee said in a video while he was traveling to parliament earlier Wednesday, per The New York Times. “President Yoon Suk Yeol has betrayed the people. President Yoon’s illegal declaration of emergency martial law is null and void. From this moment on, Mr. Yoon is no longer the president of South Korea.”

South Korean law allows martial law to be lifted with a majority vote in parliament, and Yoon compiled by 4:30 a.m. on Wednesday morning.

Sen. Chris Coons (D-Del.), a senior member of the Senate Foreign Relations Committee, offered some context to convey just how stunning Tuesday’s developments were.

“It’s literally as if the Capitol Police were around the perimeter of the Senate chamber holding off the regular Army as members [of Congress] climbed through windows to get to the floor until they got enough members on the floor to pass a resolution,” Coons told HuffPost on Tuesday. The Democratic senator was on his way to a meeting to get more details on what was happening.

He said one question he hoped to get answers to was whether there was evidence to back up Yoon’s claim that the minority party had been colluding with North Korea and undermining the security of the country.

“I’m not aware of there having been any evidence,” said Coons. “So that’s one of the things I’m asking for.”

South Korea’s main opposition party, the liberal Democratic Party, quickly called for Yoon’s resignation, pledging to impeach him if he doesn’t step down immediately.

“President Yoon Suk Yeol’s martial law declaration was a clear violation of the constitution. It didn’t abide by any requirements to declare it,” the party said in a statement on Wednesday. “His martial law declaration was originally invalid and a grave violation of the constitution. It was a grave act of rebellion and provides perfect grounds for his impeachment.”

While the Democratic Party holds a majority in the 300-seat parliament, it would require a two-thirds vote — or 200 members — to impeach him. The party currently holds 192 seats in a coalition with smaller opposition parties. The Associated Press notes, however, that when lawmakers voted to overturn his martial law decree, 10 members of Yoon’s own party voted with them.

If Yoon is removed, Prime Minister Han Duck-soo would take over his duties.

SEOUL, South Korea (AP) — South Korea’s main opposition party on Wednesday urged President Yoon Suk Yeol to resign immediately or face impeachment, hours after Yoon ended short-lived martial law that prompted troops to encircle parliament before lawmakers voted to lift it.

On Tuesday night, Yoon abruptly imposed the emergency martial law, vowing to eliminate “anti-state” forces after he struggled to push forward his agenda in the opposition-dominated parliament. But his martial law was effective for only about six hours, as the National Assembly voted to overrule the president. The declaration was formally lifted around 4:30 a.m. during a Cabinet meeting.

The liberal opposition Democratic Party, which holds a majority in the 300-seat parliament, said Wednesday that its lawmakers decided to call on Yoon to quit immediately or they would take steps to impeach him.

“President Yoon Suk Yeol’s martial law declaration was a clear violation of the constitution. It didn’t abide by any requirements to declare it,” the Democratic Party said in a statement. “His martial law declaration was originally invalid and a grave violation of the constitution. It was a grave act of rebellion and provides perfect grounds for his impeachment.”

Impeaching him would require support from two-thirds of the parliament, or 200 of its 300 members. The Democratic Party and other small opposition parties together have 192 seats. But when the parliament rejected Yoon’s martial law declaration in a 190-0 vote, about 10 lawmakers from Yoon’s ruling People Power Party cast ballots supporting the rejection, according to National Assembly officials.

If Yoon is impeached, he’ll stripped of his constitutional powers until the Constitutional Court can rule on his fate. Prime Minister Han Duck-soo, the No. 2 position in the South Korean government, would take over his presidential responsibilities.

Yoon’s martial law declaration, the first of its kind in more than 40 years, harkened to South Korea’s past military-backed governments when authorities occasionally proclaimed martial law and other decrees that allowed them to station combat soldiers, tanks and armored vehicles on streets or at public places like schools to prevent anti-government demonstrations. Such scenes of military intervention had not been seen since South Korea achieved a genuine democracy in the late 1980s until Tuesday night.

After Yoon’s declaration, troops carrying rifles and police officers were quickly deployed at parliament to ban the entrance of people, as protesters crowded outside the parliamentary compound. An Associated Press photographer saw at least three helicopters, likely from the military, that landed inside the Assembly grounds, while two or three helicopters circled above the site.

No major violence has been reported. The troops and police personnel were later seen leaving the ground of the National Assembly after the parliamentary vote to lift the martial law. National Assembly Speaker Woo Won Shik said: “Even with our unfortunate memories of military coups, our citizens have surely observed the events of today and saw the maturity of our military.”

Ruling People Power Party Han Dong-hun demanded that Yoon explain his decision and fire Defense Minister Kim Yong Hyun, who he said recommended the martial law decree to Yoon. The Defense Ministry has not commented

South Korean media reported that presidential advisers and secretaries for Yoon offered to resign and Yoon also put off his official schedule on Wednesday morning. The presidential office couldn’t immediately confirm the reports.

Under South Korea’s constitution, the president can declare martial law during “wartime, war-like situations or other comparable national emergency states” that require the use of military force to restrict the freedom of press, assembly and other rights to maintain order. Many observers question whether South Korea is currently in such a state.

The constitution also states that the president must oblige when the National Assembly demands the lifting of martial law with a majority vote.

In Washington, the White House said the U.S. was “seriously concerned” by the events in Seoul. A spokesperson for the National Security Council said President Joe Biden’s administration was not notified in advance of the martial law announcement and was in contact with the South Korean government.

Pentagon spokesman Maj. Gen. Pat Ryder said there was no effect on the more than 27,000 U.S. service members based in South Korea.

Yoon’s government and ruling party have been embroiled in an impasse with the Democratic Party over next year’s budget bill and a Democratic Party-led attempt to to impeach three top prosecutors.

During his televised announcement, Yoon also described the opposition as “shameless pro-North Korean anti-state forces who are plundering the freedom and happiness of our citizens.” He did not elaborate. North Korea has no immediate comments.

Natalia Slavney, research analyst at the Stimson Center’s 38 North website that focuses on Korean affairs, said Yoon’s imposition of martial law was “a serious backslide of democracy” that followed a “worrying trend of abuse” since he took office in 2022.

South Korea “has a robust history of political pluralism and is no stranger to mass protests and swift impeachments,” Slavney said, citing the example of former President Park Geun-hye, who was ousted from office and imprisoned for bribery and other crimes in 2017. She was later pardoned.