Manaus, Brazil. President Joe Biden has for the first time authorized the use of US-supplied long-range missiles by Ukraine to strike inside Russia, according to one US official and three people familiar with the matter.

The decision is a major US policy shift and comes as Biden is about to leave office and incoming President-elect Donald Trump has said he would bring about a swift end to the war and has expressed skepticism over continued support by the United States.

The weapons are likely to be used in response to North Korea's decision to send thousands of troops to Russia in support of Russian President Vladimir Putin's invasion of Ukraine, according to one of the people. The official and the people familiar with the matter were not authorized to discuss the decision publicly and spoke on condition of anonymity.

Ukrainian President Volodymyr Zelensky and many of his Western supporters have been pressing Biden for months to allow Ukraine to strike military targets inside Russia with Western-supplied missiles, saying the US ban had made it impossible for Ukraine to try to stop Russian attacks on its cities and electrical grids.

Some supporters have argued that this and other US constraints could cost Ukraine the war. The debate has become a source of disagreement among Ukraine’s NATO allies.

Biden had remained opposed, determined to hold the line against any escalation that he felt could draw the US and other NATO members into direct conflict with Russia.

But North Korea has deployed thousands of troops to Russia to help Moscow try to claw back land in the Kursk border region that Ukraine seized this year. The introduction of North Korean troops to the conflict comes as Moscow has seen a favorable shift in momentum. Trump has signaled that he could push Ukraine to agree to give up some land seized by Russia to find an end to the conflict.

As many as 12,000 North Korean troops have been sent to Russia, according to US, South Korean and Ukrainian assessments. US and South Korean intelligence officials say North Korea also has provided Russia with significant amounts of munitions to replenish its dwindling weapons stockpiles.

Trump, who takes office in January, spoke for months as a candidate about wanting Russia’s war in Ukraine to be over, but he mostly ducked questions about whether he wanted US ally Ukraine to win.

He also repeatedly slammed the Biden administration for giving Kyiv tens of billions of dollars in aid. His election victory has Ukraine’s international backers worrying that any rushed settlement would mostly benefit Putin.