President Joe Biden's administration has allowed Ukraine to use U.S.-made weapons to strike deep into Russia, two American officials and a source familiar with the decision said on Sunday, in a significant reversal of Washington's policy in the Ukraine-Russia conflict.

Ukraine plans to conduct its first long-range attacks in the coming days, the sources said, without revealing details due to operational security concerns.

The move comes two months before president-elect Donald Trump takes office on Jan. 20 and follows months of pleas by Ukrainian President Volodymyr Zelenskyy to allow Ukraine's military to use U.S. weapons to hit Russian military targets far from its border.

"Today, many in the media are saying that we have received permission to take appropriate actions," Zelenskyy said in a Sunday evening address.

"But strikes are not made with words. Such things are not announced. The missiles will speak for themselves."

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The change comes largely in response to Russia's deployment of North Korean ground troops to supplement its own forces, a development that has caused alarm in Washington and Kyiv, a U.S. official and a source familiar with the decision said.

The White House and the U.S. State Department declined to comment. The Ukrainian Foreign Affairs Ministry and president's office did not immediately respond to requests for comment.

Russia has warned that it would see a move to loosen the limits on Ukraine's use of U.S. weapons as a major escalation.

Ukraine's first deep strikes are likely to be carried out using ATACMS rockets, which have a range of up to 306 kilometres, according to the sources.

While some U.S. officials have expressed skepticism that allowing long-range strikes will change the war's overall trajectory, the decision could help Ukraine at a moment when Russian forces are making gains and possibly put Kyiv in a better negotiating position when and if ceasefire talks happen.

It is not clear if Trump will reverse Biden's decision when he takes office. Trump has long criticized the scale of U.S. financial and military aid to Ukraine and has vowed to end the war quickly, without explaining how.

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Some Ukrainians are expressing uneasiness that Donald Trump’s U.S. election win could mean an end to the country's support against Russia. Trump has publicly criticized sending Ukraine billions in military aid, and has said he could make a deal to ‘end the war in a day.’

A Trump spokesperson did not immediately respond to a request for comment. But one of his closest foreign policy advisers, Richard Grenell, criticized the decision.

"Escalating the wars before he leaves office," Grenell said, in an X post responding to the news.

Some congressional Republicans had urged Biden to loosen the rules on how Ukraine can use U.S.-provided weapons.

Since Trump's Nov. 5 election victory, senior Biden administration officials have repeatedly said they would use the remaining time to ensure Ukraine can fight effectively next year or negotiate peace with Russia from a "position of strength."

'Way too late'

The U.S. believes more than 10,000 North Korean soldiers have been sent to eastern Russia and that most of them have moved to the Kursk region and have begun to engage in combat operations.

Russia is advancing at its fastest rate since 2022 despite taking heavy losses, and Ukraine said it had clashed with some of those North Korean troops deployed to Kursk.

Stretched by personnel shortages, Ukrainian forces have lost some of the ground they captured in an August incursion into Kursk that Zelenskyy said could serve as a bargaining chip.

"Removing targeting restrictions will allow the Ukrainians to stop fighting with one hand tied behind their back," Alex Plitsas, senior non-resident fellow at the Atlantic Council, said.

"However, like everything else, I believe history will say the decision came way too late. Just like the ATACMS, HIMARS, Bradley Fighting Vehicles, Abrams Tanks and F-16. They were all needed much sooner," he said.

Despite Zelenskyy's pleas, the White House had been reluctant to allow U.S.-supplied weapons to be used to strike targets deep inside Russia for fear this could escalate the conflict.

Kyiv's other allies have been supplying weapons but with restrictions on how and when they can be used inside Russia, out of concern such strikes could prompt retaliation that draws NATO countries into the war or provokes a nuclear conflict.

Poland's foreign affairs minister, Radoslaw Sikorski, also called the move a response to North Korea's involvement.

"President Biden responded to the entry of North Korean troops into the war and the massive Russian missile strike in a language that V. Putin understands — by removing restrictions on Ukraine's use of Western missiles," Sikorski said on X.