House Intelligence Committee Chair Mike Turner (R-Ohio) on Wednesday said the U.S. should consider taking “direct military action” if North Korean troops enter the war in Ukraine, following the revelation that thousands of soldiers from the isolated country are in Russia.

The White House said earlier Wednesday that Washington had assessed at least 3,000 North Korean troops are undergoing training at military bases in eastern Russia, with fears they will eventually be sent to Ukraine to fight alongside Kremlin forces.

Defense Secretary Lloyd Austin said Tuesday the U.S. has seen evidence that North Korean troops were in the former Soviet state.

“The Biden-Harris Administration must make clear that North Korean troops entering this conflict are a red line for the United States,” Turner said in a statement.

“If North Korean troops were to invade Ukraine’s sovereign territory, the United States needs to seriously consider taking direct military action against the North Korean troops,” he added.

Between early to mid-October, North Korea moved at least 3,000 soldiers into eastern Russia via ships from the Wonsan region in North Korea to the eastern Russian city of Vladivostok, White House national security spokesperson John Kirby told reporters.

The soldiers then traveled onward to three military sites in eastern Russia where they are undergoing basic combat training, Kirby said. 

“We do not yet know whether these soldiers will enter into combat alongside the Russian military, but this is certainly a highly concerning probability,” he said.

He added that after completing training, the soldiers could travel to western Russia and then engage in combat against the Ukrainian military, a development that would “demonstrate Russia’s growing desperation in its war against Ukraine.” 

The U.S. has briefed the Ukrainian government on the situation, to include the implications of such a move and how the U.S. might respond, according to Kirby.

He also gave a stark warning that should the North Korean troops be employed against Ukraine, “they will become legitimate military targets.”

“If they do deploy to fight against Ukraine, they’re fair game, they’re fair targets, and the Ukrainian military will defend themselves against North Korean soldiers the same way they’re defending themselves against Russian soldiers,” he said. 

Ukrainian President Volodymyr Zelensky last week warned that North Korea was sending close to 10,000 troops to Ukraine to fight for Russian forces. Speaking in Brussels, Belgium, Zelensky said Pyongyang had already sent tactical personnel and officers to his country.

Reports of the North Korean troops on the brink of possibly entering the fight have ignited calls for the U.S. to lift restrictions on the use of long-range weapons given to Ukraine, with Zelensky repeatedly calling on Washington to do so.

“I have long challenged the Biden-Harris Administration’s unwise position on restricting Ukraine’s use of U.S. weapons against targets within Russian territory,” Turner said in his statement. “If North Korean troops attack Ukraine from Russian territory, Ukraine should be permitted to use American weapons to respond.”

Asked why the U.S. would not greenlight long-range missiles for Ukraine, Kirby replied that it is still up in the air whether the North Korean soldiers would be deployed into combat, and it was too early to tell the kind of impact they would have on the battlefield.

“We don’t know what they’re going to do, we don’t know if they’re going to deploy into combat or not, we don’t know if they do at what strength,” he said, adding that the U.S. will monitor the situation closely and continue to surge security assistance to Kyiv.

North Korean troops fighting for Russia in Ukraine would mark a monumental step up in relations between the two countries, after Russian President Vladimir Putin and North Korean leader Kim Jong Un signed a partnership and pledged to provide mutual aid and protection against foes in June. 

Pyongyang also has been providing Moscow artillery shells and ballistic missiles in exchange for access to aid and technology for nuclear and space programs.