The United States is "highly concerned" about North Korea's reported dispatch of troops to support Russia in its war against Ukraine, a White House official said Friday, noting that Washington will consult with allies on the implications of "such a dramatic move" if the report is true.

On Friday, Korea time, South Korea's National Intelligence Service confirmed the North has decided to send around 12,000 troops to support Russia in the war and has already begun deployment of approximately 1,500 soldiers to Vladivostok.

"We are highly concerned by reports of DPRK soldiers fighting on behalf of Russia," National Security Council spokesperson Sean Savett said in response to a question from Yonhap News Agency. DPRK stands for the North's official name, the Democratic People's Republic of Korea.

"We are unable to confirm whether these reports are accurate, but if true, this would mark a dangerous development in Russia's war against Ukraine. If the DPRK joins Russia, we will consult with our allies and partners on the implications of such a dramatic move," he added.

The US' refusal to confirm the deployment followed Seoul's confirmation of it, raising questions over whether the allies differ on intelligence analysis.

Savett noted that the North's troop deployment, if true, would indicate Russia's "growing desperation" as Russia continues to suffer "extraordinary" casualties on the battlefield in its war against Ukraine.

"If Russia is indeed forced to turn to the DPRK for manpower, this would be a sign of desperation, not strength, on the part of the Kremlin," he said.

Russia is known to have been averaging more than 1,200 casualties per day in recent months.

The spokesperson's remarks are similar to those made earlier by White House National Security Communications Advisor John Kirby and State Department spokesperson Matthew Miller. (Yonhap)