The soldier is believed to be the first North Korean prisoner of war captured since Pyongyang deployed forces to support Russia’s war in Ukraine.

South Korea’s National Intelligence Service said it had confirmed through an “allied intelligence agency” that the soldier had died from “serious injuries”, Yonhap reported.

North Korea has sent more than 10,000 soldiers to help Russia, according to Kyiv and Seoul – though Moscow and Pyongyang have neither confirmed nor denied their presence.

The spy agency earlier confirmed that Ukrainian forces had captured the soldier after a photo purporting to show the man had been circulating on Telegram.

“This is the first in a string of captures and killings,” Yang Uk, a research fellow at the Asan Institute for Policy Studies, told the BBC. “For Ukrainians, it’s more beneficial to capture these North Korean troops and try to exchange them with Russians for Ukrainian prisoners of war.”

Recent images emerging from the Russia-Ukraine war confirmed speculations that “North Korean troops will be deployed in large numbers to the assault by Russian command”, Mr Yang said.He also added, however, that “it will be challenging to prove their North Korean nationality”.

Ukrainian forces say that North Korean soldiers have been issued with fake Russian IDs, while Ukrainian President Volodymyr Zelensky posted footage last week which he said showed Russian troops burning the faces of slain North Koreans to conceal their identities.

Ukrainian and South Korean intelligence services have said that many of the troops deployed to Russia are some of Pyongyang’s best, drawn from the 11th Corps, also known as the Storm Corps. The unit is trained in infiltration, infrastructure sabotage and assassinations.

More than 3,000 North Korean troops have died or been wounded while fighting in Russia’s Kursk region, Zelensky said Monday.

He added that the collaboration between Moscow and Pyongyang heightened the “risk of destabilisation” around the Korean peninsula.

Russia launched a full-scale invasion of Ukraine in February 2022. The recent deployment of North Korean troops to Russia is a sign of a growing alliance between the two pariah states.

The development, which comes as North Korea ratchets up tensions with South Korea, has sparked worries in the West. China, a long-standing ally of both sides, is also keeping a cautious eye on the friendship.

Lee Sung-kwon, speaking to reporters after parliament was briefed by the country’s National Intelligence Service, said another 1,000 had been injured.

He said the casualties included high-ranking officials, and could be explained by the troops lack of familiarity with the terrain, and with drone warfare.

The first reports of North Korean casualties came earlier this week. It emerged in October that the North had sent 10,000 troops to help Russia’s war effort.

On Monday a US Pentagon spokesman said North Koreans had been killed, without giving a number, and a day later an unnamed US official said that there had been “several hundred” killed or wounded.

Mazzaltov World News has not independently verified the claims.

The North Korean troops, none of whom will have any previous combat experience, are believed to have spent their first weeks in Russia in training and then in support roles.

The casualties are thought to have occurred in Russia’s Kursk region, where Ukrainians are defending a small area of territory captured during a surprise incursion in August.

Last Saturday, Ukrainian President Volodymyr Zelensky said Russia had begun to use a “significant number” of North Koreans in its assaults in Kursk.

They are not thought to have been deployed in Ukraine itself, where Russian troops have been advancing in eastern parts of the country in recent months.

Lee Sung-kwon said there were reports of preparations for additional deployment, and that North Korean leader Kim Jong-un could oversee training.

He quoted intelligence officials as saying the high number of casualties could be attributed to an “unfamiliar battlefield environment, where North Korean forces are being utilised as expendable frontline assault units, and their lack of capability to counter drone attacks”.

“Within the Russian military, complaints have reportedly surfaced that the North Korean troops, due to their lack of knowledge about drones, are more of a burden than an asset,” he added.

Neither Russia nor the North have acknowledged the troop deployments, but a North Korean statement on Thursday carried by state news agency KCNA said the country’s alliance with Moscow was “deterring the US and the West’s ill-intended extension of influence”.