LONDON — Ukrainian President Volodymyr Zelenskyy said Monday that more than 3,000 North Korean soldiers are believed to have been killed or wounded fighting for Moscow in Russia’s western Kursk region.

Zelenskyy posted to Telegram on Monday following a briefing by Kyiv’s top commander — Gen. Oleksandr Syrskyi — on the ongoing battle in Kursk, underway since Ukrainian troops launched a surprise cross-border incursion there in August.

“There are risks of sending additional soldiers and military equipment to the Russian army from North Korea,” Zelenskyy said, vowing “tangible responses” to any such move. “According to preliminary data, the number of killed and wounded North Korean soldiers in the Kursk region already exceeds 3,000 people.”

Ukrainian special forces claimed on Monday to have inflicted more than 100 casualties among North Korean forces over three days of operations.

Ukraine’s Special Operations Forces branch claimed in a post to its official Telegram channel that 77 North Koreans were killed and 40 wounded in recent fighting.

On Sunday, the SSO posted photos of what it said were North Korean troops killed in Russia’s western Kursk region. The SSO also uploaded photos of purportedly fabricated Russian military identity cards. ABC News was not immediately able to independently verify the images.

“Russia is trying to hide the presence of military personnel from North Korea by issuing them with fake documents,” the SSO wrote.

It added that the documents “do not have all the seals, photographs, the patronymics are given in the Russian manner and the place of birth is signed as the Republic of Tuva,” the home region of Sergei Shoigu — formerly Russia’s defense minister and now the secretary of the Security Council.

The SSO said the signatures of the document owners were written in Korean, which it said “indicates the real origin of these soldiers.”

U.S., South Korean and Ukrainian officials have said there are currently up to 12,000 North Korean soldiers inside Russia, deployed there primarily to help push Kyiv’s forces out of positions taken in Kursk.

Ukrainian military sources told ABC News in November that North Koreans were expected to be among the 50,000 troops arrayed for a major counter-offensive in Kursk.

The deployment of troops marks a new milestone in North Korean support for Russia’s war, Pyongyang already having supplied Moscow with ammunition and weapons — including ballistic missiles — since the full-scale invasion began in February 2022.

Ukrainian President Volodymyr Zelenskyy said earlier this month that Kyiv has “preliminary data that the Russians have begun to use North Korean soldiers in their assaults — a significant number of them.”

The Ukrainian Defense Ministry’s Main Directorate of Intelligence, meanwhile, has reported “significant casualties” among North Korean troops deployed on the front lines alongside Russian units.

South Korea’s Yonhap news agency reported on Monday that Seoul expects Pyongyang to send more troops and equipment to Russia.

“North Korea is preparing to rotate or increase the deployment of troops [in Russia], while currently supplying 240mm rocket launchers and 170mm self-propelled artillery,” said South Korea’s Joint Chiefs of Staff, as quoted by Yonhap.

“There are also some signs of [the North] moving to manufacture and supply suicide drones,” the JCS said.

North Korean leader Kim Jong Un visited a drone production and test facility in November. Then, the state-run Korean Central News Agency said Kim “underscored the need to build a serial production system as early as possible and go into full-scale mass production.”