MANAUS, Brazil — President Joe Biden has authorized Ukraine to use U.S.-supplied long-range missiles to strike deeper inside Russia, easing limitations on the weapons as Russia deploys thousands of North Korean troops to reinforce its war, according to a U.S. official and three other people familiar with the matter.

The decision allowing Kyiv to use the Army Tactical Missile System, or ATACMs, for attacks farther inside Russia comes as President Vladimir Putin positions North Korean troops along Ukraine’s northern border to try to reclaim hundreds of miles of territory seized by Ukrainian forces.

Meanwhile, Russia launched a massive drone and missile attack Sunday across Ukraine, described by officials as the largest in recent months, targeting energy infrastructure and killing civilians.

President Volodymyr Zelenskyy said Russia launched 120 missiles and 90 drones in a large-scale attack. Various types of drones were deployed, he said, including Iranian-made Shaheds, as well as cruise, ballistic and aircraft-launched ballistic missiles.

Ukrainian defenses shot down 144 out of 210 air targets, Ukraine’s air force reported later Sunday.

Biden’s move to allow longer strikes also follows the win by President-elect Donald Trump, who has said he would bring about a swift end to the war after he takes office Jan. 20 and raised uncertainty about whether his administration would continue the United States’ vital military support for Ukraine.

The official and the others knowledgeable about the matter were not authorized to discuss the U.S. decision publicly and spoke on condition of anonymity.

Zelenskyy’s reaction Sunday to Biden’s move was restrained. “Strikes are not made with words,” he said during his nightly video address. “Such things are not announced. The missiles will speak for themselves.”

Zelenskyy and many of his Western supporters have been pressing Biden for months to allow Ukraine to strike military targets deeper inside Russia with Western-supplied missiles, saying the U.S. ban had made it impossible for Ukraine to try to stop Russian attacks.

“And this is the answer to everyone who tried to achieve something with Putin through talks, phone calls, hugs and appeasement,” Zelenskyy said.

His statement came shortly after he posted a message of condolence on Telegram after a Russian attack on a nine-story building that killed at least eight people in the northern city of Sumy, 24 miles from the border with Russia.

Some have argued that the limitation and other U.S. 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 U.S. and other NATO members into direct conflict with nuclear-armed Russia.

News of Biden’s decision followed meetings over the past two days with the leaders of South Korea, Japan and China. The addition of North Korean troops was central to the talks, which took place on the sidelines of the Asia-Pacific Economic Cooperation summit in Peru.

Biden did not mention the decision during a speech at a stop in the Amazon rainforest in Brazil on his way to the Group of 20 summit.

The longer-range missiles are likely to be used in response to North Korea’s decision to support Putin’s invasion of Ukraine, according to one person familiar with the development.

Some backers of Ukraine say that even a few long-range strikes deeper into Russia would force its military to alter deployments and expend more resources.

North Korea has provided as many as 12,000 troops to Russia to help Moscow try to claw back land in the Kursk border region that Ukraine seized this year.

When Russian tanks rolled into Ukraine in February 2022, the conventional wisdom was that the capital would soon fall and the rest of the country wouldn’t last long against a larger enemy.

Instead, it was that narrative that quickly collapsed. The Ukrainian army proved it could slow the advance of Russia’s forces and, if not drive them out completely, then — with enough support from the West — at least forestall defeat.

But nearly three years later, the outlook is again grim.

Russia is expending huge amounts of weaponry and human life to make small-but-steady territorial gains to the nearly one-fifth of Ukraine it already controls. Ukraine, meanwhile, is struggling to minimize losses, maintain morale and convince allies that, with more military aid, it can turn the tide.

As this brutal war of attrition grinds toward its 1,000th day this week, neither side seems eager to negotiate. Trump has said he could quickly end the war, but it’s unclear how or in whose favor he might tip the scales. This backdrop appears to be driving Russia’s strategy in eastern Ukraine, according to Phillips O’Brien, a professor of strategic studies at the University of St. Andrews, Scotland.

Trump could try to force an end to the war by halting the supply of weapons.

“If Trump cuts aid to Ukraine and a cease-fire leads to a frozen conflict, Russia wants to secure as much territory as it can now,” O’Brien said.

For Ukraine, the key to a cease-fire would be guarantees from the West that it won’t allow Russia to re-invade. Otherwise, O’Brien said, “a cease-fire is a recipe for constant instability in Europe.”