North Korean troops sent to Russia in support of its war against Ukraine have reportedly crossed the border into Ukraine.

Citing a Ukrainian security source and military spokesperson on Friday, CNN reported that North Korean "technical advisers" arrived in Ukraine's southeastern Mariupol region that is occupied by Russia.

While the purpose of their visit is unclear, they were wearing the Russian military uniform, according to the source.

Other North Korean soldiers were seen at another front line region of Kharkiv in northeastern Ukraine.

A Ukrainian military official said North Korean troop presence in Kharviv was verified through radio monitoring.

While it was previously reported that an estimated eleven-thousand North Korean troops were sent to Russia's Kursk region, the expanded scope of deployment into Ukrainian territory could signal Pyongyang's deeper participation in the conflict.