Russia on Thursday rejected a recent South Korean claim that North Korean soldiers were likely fighting alongside Russian forces in Ukraine.

During a parliamentary audit session in Seoul on Tuesday, South Korean Defense Minister Kim Yong-hyun said it was "highly likely" that North Korea had deployed troops in support of Russia, because the two countries have a mutual treaty "akin to a military alliance."

Kim also said a recent media report on North Korean troop casualties in a Russian-occupied territory near the eastern Ukrainian city of Donetsk is also likely to be true.

On Thursday, however, Russian state media TASS quoted presidential spokesperson Dmitry Peskov as saying, "It looks like another piece of fake news."

On June 19, North Korea and Russia signed a comprehensive strategic partnership agreement, which calls for mutual assistance in the event of aggression against either country.

The Pentagon has also said this week that it continues to monitor North Korea's military support for Russia. (Yonhap)