WASHINGTON >> The U.S. said Wednesday that 3,000 North Korean troops have deployed to Russia and are training at several locations, calling the move very serious and warning that those forces will be “fair game” if they go into combat in Ukraine.

The deployment raises the potential for the North Koreans to join Russian forces in Ukraine and suggests expanded military ties between the two nations as Moscow seeks weapons and troops to gain ground in a grinding war that has stalemated after more than two years.

Defense Secretary Lloyd Austin called it a “next step” after the North has provided Russia with arms, and said Pyongyang could face consequences for aiding Russia directly. His comments were the first public U.S. confirmation of North Korea sending troops to Russia — a development South Korean officials disclosed but was denied by Pyongyang and Moscow.

White House national security spokesman John Kirby said the U.S. believes that at least 3,000 North Korean soldiers traveled by ship to Vladivostok, Russia’s largest Pacific port, in early to mid-October.

“These soldiers then traveled onward to multiple Russian military training sites in eastern Russia, where they are currently undergoing 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.”

Kirby said they could go to western Russian and then engage in combat against Ukraine’s forces, but both he and Austin said the U.S. continues to assess the situation.

Exactly what the North Korean troops are doing in Russia was “left to be seen,” Austin told reporters in Rome.

He added: “If they’re co-belligerents, 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.”

Kirby warned, however, that “I can tell you one thing, though, if they do deploy to fight against Ukraine, they’re fair game.”

He said a key question is what North Korea’s leader Kim Jong Un is getting out of this.

Russia and North Korea have sharply boosted their cooperation in the past two years, and in June they signed a major defense deal requiring both countries to use all available means to provide immediate military assistance if either is attacked.

South Korean officials worry that Russia may reward North Korea by giving it sophisticated weapons technologies that could boost its nuclear and missile programs that target South Korea. South Korea said Tuesday it would consider supplying weapons to Ukraine in response to the reported troop dispatch.

South Korea’s spy chief had told lawmakers that 3,000 North Korean troops are now in Russia receiving training on drones and other equipment before being deployed to battlefields in Ukraine.