The United States claims to have evidence that North Korea has sent 3,000 troops to Russia, according to a Reuters report.

At the same time, South Korea reports that North Korea has pledged a total of 10,000 troops to Russia.

U.S. officials are concerned that these troops may be deployed to Ukraine to support Russia in the ongoing war. However, both Moscow and Pyongyang have denied this, according to the report.

U.S. Defense Secretary Lloyd Austin stated that if North Korean troops were indeed sent, it would represent a “very, very serious” development.

The U.S. evidence indicates that the North Korean troops are stationed across three military bases in eastern Russia.

The Reuters report details that the troops traveled by ship from North Korea’s Wonsan region to the eastern Russian city of Vladivostok in mid-October.

Moscow and Pyongyang signed a mutual defense treaty at a summit in June where they pledge to boost military ties, but have dismissed the reports about North Korean troops being trained in Russia as “fake news” and “groundless rumors.”