Austin is the first U.S. official to confirm reports from Ukrainian and South Korean leaders about the North Korean troop movements.

“We are seeing evidence that there are North Korean troops that have gone to Russia,” he told reporters traveling with him Wednesday in Rome. “What, exactly, they’re doing is left to be seen.”

Austin did not specify how many troops the U.S. believed had traveled to Russia and whether any had been deployed to Ukraine. There have been differing reports that anywhere from 1,500 to 12,000 soldiers have been dispatched. Ukrainian President Volodymyr Zelensky told a NATO Summit last week that North Korea could be providing Russia with “10,000” soldiers and technical personnel.

“If they’re a cobelligerent, their intention is to participate in this war on Russia’s behalf. That is a very, very serious issue, and it will have impacts not only in Europe. It will also impact things in the Indo-Pacific as well,” Austin added.

It’s unclear what North Korea will get in exchange for providing troops to Russia.

Pentagon spokesman Maj. Gen. Patrick Ryder has not confirmed whether the U.S. has seen intelligence indicating North Korean troops had deployed to Russia on Tuesday afternoon but said if it were to happen, it would “mark a dangerous and highly concerning development.” 

“Clearly, North Korea and Russia have a relationship,” he added. “As to the eaches [sic] of that relationship and the kinds of exchanges of information and training that they’ve had over the years, you know, that — that in and of itself is not something that’s necessarily new. But obviously, we’re continuing to keep a close eye on this as it relates to the situation in Ukraine.”

The U.S. has repeatedly warned against adversaries coming to Russia’s aid for its war in Ukraine, but Moscow has been able to strengthen its relationships with Tehran, Beijing, and Pyongyang.

Iran has provided Russia with hundreds of kamikaze drones, sent it ballistic missiles, and has helped it set up its own factory to build more of these drones, while North Korea has provided it with artillery and now troops.

North Korea’s decision to provide troops to Ukraine comes only weeks before the U.S. presidential election, where continued U.S. aid to Ukraine is effectively on the ballot.

Vice President Kamala Harris has indicated she’s in lockstep with President Joe Biden’s continued aid to Ukraine, while former President Donald Trump described Biden last month as “the greatest salesman on Earth” due to continued U.S. support for Ukraine.