The defense ministry said Wednesday it is "closely" monitoring for signs of North Korea possibly sending troops to support Russia in its war against Ukraine, following media reports of Russia forming a battalion of North Koreans.

Ukrainian media outlets earlier reported that Russia is organizing a special battalion that is expected to include up to 3,000 North Koreans due to manpower shortages amid concerns over deepening military cooperation between the two countries.

"As there is a possibility of (North Korea) providing troops or civilian personnel, this is being closely monitored," a ministry official said when asked about the reports.

The National Intelligence Service also said it is working to verify the reports while keeping in mind that "the reports may be true."

"(We) are also cooperating with Ukraine to confirm the reports," the spy agency said.

A foreign ministry official said the government is monitoring signs of military cooperation between Russia and North Korea, and noted Seoul's "deep concern" over the reports of the cooperation expanding beyond arms trade to troop deployment.

"Any cooperation that indirectly or directly helps North Korea strengthen its military force is a violation of U.N. Security Council resolutions," the official said. "(We) once again urge for the halt to the illegal military cooperation between Russia and North Korea."

South Korea, the United States and others have accused North Korea of supplying arms to Russia to fuel its war in Ukraine in violation of U.N. Security Council resolutions against the North over its missile and nuclear programs.

Last week, Defense Minister Kim Yong-hyun told lawmakers that the North is likely to deploy troops to Ukraine in support of Russia, after Ukrainian media reported that six North Koreans were killed in a Ukrainian missile strike on Russian-occupied territory earlier this month.

Moscow and Pyongyang have recently forged closer ties, with President Vladimir Putin and North Korean leader Kim Jong-un signing a new partnership treaty that includes a mutual defense clause during their summit in Pyongyang in June. (Yonhap)