President Biden approved Ukraine's military to use U.S.-provided long-range missiles on targets inside Russian territory, the New York Times reported Sunday, citing unnamed U.S. officials.

Russian President Vladimir Putin has previously said that such an escalation would constitute an act of war. He has yet to react to Biden's announcement Sunday.

The White House did not immediately respond to a request for comment from Fox News Digital.

Biden's announcement came just hours after Russia concluded one of its largest missile and drone attacks in months, launching over 200 targeting Ukraine's power and energy infrastructure.

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Putin has previously said that giving Ukraine the green light on missile use would effectly mean that the U.S. and NATO are "in the war."

"Flight assignments for these missile systems can, in fact, only be entered by military personnel from NATO countries. Ukrainian servicemen cannot do this. And therefore, it is not a question of allowing the Ukrainian regime to strike Russia with these weapons or not. It is a question of making a decision whether NATO countries directly participate in the military conflict or not," Putin in September.

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"If this decision is made, it will mean nothing less than the direct participation of NATO countries, the United States, and European countries, in the war in Ukraine," he added.

Meanwhile, President-elect Trump's transition team is expected to soon announce a peace envoy to assist in negotiations between Ukraine and Russia. Trump argued on the campaign trail that he could solve the conflict before entering office.

Trump has been rolling out appointee names of those he wants to fill his Cabinet and advise him on top issues at a lightning-quick pace.

Some advisers are reportedly encouraging Trump to push Kyiv to agree to terms that would freeze the frontlines by creating an 800-mile-long demilitarized zone and allow Russia to keep the land it has illegally seized, which amounts to roughly 20% of Ukraine.

It has also been suggested that Kyiv should agree not to pursue NATO membership for 20 years, a stipulation that critics of this plan argue kowtows to Putin.

This is a developing story. Check back soon for updates.