SEOUL, South Korea (AP) — A former South Korean defense minister was formally arrested Wednesday over his alleged collusion with President Yoon Suk Yeol and others in imposing martial law last week, as authorities investigate whether their acts amount to rebellion.

Martial law, the first in more than 40 years, lasted only about six hours but has triggered a domestic firestorm and large street protests. Yoon and his associates face criminal investigations and impeachment attempts. The Justice Ministry has banned Yoon and eight others from leaving the country as authorities see them as key suspects in the martial law case. It’s the first time that a sitting president in South Korea has received a travel ban.

The Seoul Central District Court said it approved an arrest warrant for former Defense Minister Kim Yong Hyun on charges of rebellion and abuse of power.

Kim has been detained since Sunday. Prosecutors have up to 20 days to determine whether to indict him. A conviction on the charge of rebellion carries a maximum death sentence.

Kim became the first person arrested over the case. He has been accused of recommending martial law to Yoon and sending troops to the National Assembly to block lawmakers from voting on it. Enough lawmakers eventually managed to enter a parliament chamber and unanimously rejected Yoon’s decree, forcing the Cabinet to lift it before daybreak on Dec. 4.

Kim said in a statement Tuesday that he “deeply apologizes for causing significant anxiety and inconvenience.” He said all responsibility for the imposition of martial law rests solely with him and pleaded for leniency for soldiers deployed to enforce it, saying they were only following his order.

Prosecutors reportedly accuse Kim of playing a key role in a rebellion and committing abuse of power by staging a riot to disrupt the constitution in collaboration with Yoon and other military and police officers. Prosecutors’ offices in Seoul couldn’t immediately confirm the reports.

The opposition-controlled parliament passed a bill Tuesday to appoint an independent special counsel to investigate Yoon and other top military officials over the martial law introduction. The main opposition Democratic Party had advocated for a special counsel investigation, arguing that public prosecutors cannot be trusted to conduct a thorough investigation of Yoon, a former prosecutor-general.

During a parliamentary hearing Tuesday, Kwak Jong-keun, commander of the Army Special Warfare Command whose troops were sent to parliament, testified that he received direct instructions from Kim Yong Hyun to obstruct lawmakers from entering the National Assembly’s main chamber. Kwak said the purpose of Kim’s instructions was to prevent the 300-member parliament from gathering the 150 votes necessary to overturn Yoon’s martial law order.

Kwak said Yoon later called him directly and asked for the troops to “quickly destroy the door and drag out the lawmakers who are inside.” Kwak said he discussed Yoon’s order with the commander at the scene and that they concluded there was nothing that could be done, ruling out the possibility of threatening the lawmakers by shooting blanks or cutting off electricity.

At the same hearing, senior officer Kim Dae-woo of the military’s counterintelligence agency said his commander, Yeo In-hyung, asked him if an army bunker in Seoul had space to detain politicians and other figures after martial law was imposed. Yeo is considered a close associate of Kim Yong Hyun. Last week, Hong Jang-won, a deputy director of the country’s spy agency, said Yoon ordered him to help Yeo’s command to detain some of his political rivals but he ignored the president’s order.

Kwak and Yeo are among those who face opposition-raised rebellion charges along with Yoon and Kim, and the Defense Ministry suspended them last week.

Opposition parties and many experts say the martial law decree was unconstitutional. They say a president is by law allowed to declare martial law only during “wartime, war-like situations or other comparable national emergency states” and South Korea wasn’t in such a situation. They argue that deploying troops to seal the National Assembly to suspend its political activities amounted to rebellion because the South Korean Constitution doesn’t allow a president to use the military to suspend parliament in any situation.

In his martial law announcement, the conservative Yoon stressed a need to rebuild the country by eliminating “shameless North Korea followers and anti-state forces,” a reference to his liberal rivals who control parliament.

Yoon avoided impeachment on Saturday after most governing party lawmakers boycotted a floor vote in the National Assembly.

The Democratic Party said it would prepare for a new vote on Yoon’s impeachment on Saturday. The party on Tuesday submitted motions to impeach Yoon’s police chief and justice minister as well. It pushed to impeach Kim Yong Hyun and the safety minister, but they resigned before parliament took a vote.

If Yoon is impeached, his presidential powers would be suspended until the Constitutional Court decides whether to restore his powers or remove him from office. If it voted for removal, a new presidential election would be required.