North Korean soldiers hold national flags of North Korea, in this photo released by the Korean Central News Agency, Oct. 16. Yonhap

Some 10,000 North Korean troops have been deployed in Russia, with a "considerable" number of them having been dispatched to front-line areas, South Korea's defense ministry said Tuesday.

The assessment came amid concerns that North Korean troops may join Russian forces for combat in Russia's western border region of Kursk in the coming days.

"More than 10,000 North Korean troops have currently gone to Russia, and we understand that a considerable number of them have moved to front-line areas, including Kursk," Jeon Ha-kyou, a spokesperson at the ministry, told a press briefing.

Jeon said he did not have any new information about North Korean troop activity but noted that South Korea's military and intelligence authorities are closely monitoring the situation in Ukraine.

On Monday, a U.S. State Department spokesperson said as many as 10,000 North Korean troops were in the Kursk region and could engage in combat in the "coming days." (Yonhap)