"It could be a game changer. The longer Ukraine can strike, the shorter the war will be," Sybiga told reporters ahead of a UN Security Council meeting to mark 1,000 days since the Russian invasion of its pro-Western neighbor.

He argued that Kyiv has the "full right to strike military targets on the territory of Russia."

"It could have a very positive impact on the situation on the battlefield," Sybiga added.

Biden approved the use of long-range US missiles, long sought by Ukraine, two months before he leaves office to be replaced by US President-elect Donald Trump, who is seen as less inclined to help Kyiv.

Russia on Monday accused Biden of fueling tensions with the move.

UN Under-Secretary-General for Political Affairs Rosemary DiCarlo, referring to the green light, said that "all parties must ensure the safety and protection of civilians, regardless of their location."

DiCarlo, speaking on behalf of UN Secretary-General Antonio Guterres, went on to mark the "1,000 days of widespread death, destruction and despair that continue unabated for millions of Ukrainians."

She denounced the rise in civilian casualties and Russia's attack on Ukraine over the weekend, involving 120 missiles and 90 drones, which caused significant damage to Ukraine's power grid.

"The targeted devastation of Ukraine's energy infrastructure may make the coming winter the harshest since the start of the war," she warned.

US ambassador Linda Thomas-Greenfield, without mentioning the long-range missile issue, reiterated American support for Ukraine.

"The United States will continue to surge security assistance to Ukraine, including artillery, air defense, armored vehicles and other needed capabilities and munitions, and we will announce additional security assistance for Ukraine in the days to come," she said.

"The Kremlin wants to plunge Ukraine into darkness. But we must stand for the light of its freedom," said British Foreign Secretary David Lammy. "One thousand days in, we still stand for Ukraine."

Russian ambassador Vassily Nebenzia dismissed Monday's UN meeting on the Ukraine war as "just a good media opportunity to demonize Russia."