The United States and Russia traded barbs Monday over President Joe Biden's reported decision to allow Ukraine to use US-provided longer-range missiles to strike targets inside Russia, amid concerns about an escalation of Moscow's protracted war in Ukraine.

US officials repeated accusations that Russia was to blame for an escalation in the wake of its introduction of North Korean troops onto the battlefield, while the Kremlin accused the Biden administration of moving to "continue adding fuel to the fire."

Citing officials in Washington, The New York Times reported Sunday that Biden has authorized the first use of the missiles, known as Army Tactical Missile Systems, for strikes inside Russia -- a major policy shift just two months before he leaves office. Washington declined to officially confirm the report.

"When you look at escalation of this conflict, it has been Russia that has escalated the conflict time and time again, and that includes just in the recent month when Russia recruited the deployment of more than 11,000 North Korean soldiers who are now on the front lines in Kursk, engaging in combat operations against the Ukrainian military," Matthew Miller, the State Department spokesperson, told a press briefing.

"That is a major escalation by Russia bringing in an Asian military to a conflict inside Europe, and as we said, as the secretary said, our response to that would be firm and the supporters of Ukraine's response to that need to be firm," he added.

In a press meeting, US Deputy National Security Advisor Jon Finer struck the same note.

"I will say, with regard to the comments that came out of Russia, the fire was lit by Russia's invasion of Ukraine. I think this notion of fuel on the fire is, frankly, a side issue to the main issue, which is Russia waging a war of aggression across a sovereign border into Ukraine, and continuing to do so," Finer said according to a transcript provided by the White House.

"We've seen, in addition to the North Korean forces deployment that I mentioned, a major escalation in terms of an aerial attack on infrastructure across Ukraine over the last 24 hours. So, I would put the question back to Russia about who's actually putting fuel on the fire here, and I don't think it's the Ukrainians."

Earlier in the day, the Kremlin warned against the reported decision to allow Ukrainians to launch strikes inside Russia.

"It is obvious that the outgoing administration in Washington intends to take steps and they have been talking about this, to continue adding fuel to the fire and provoking further escalation of tensions around this conflict," spokesman Dmitry Peskov was quoted by the Associated Press as saying.

The exchange of barbs came as Seoul and Washington have been consulting over measures to take in response to the North's troop deployment amid concerns that Pyongyang's troop dispatch to the Kursk region could expand the conflict with security implications for both Europe and the Indo-Pacific. (Yonhap)