For the first time, President Biden has given Ukraine the green light to use powerful American long-range weapons for strikes inside Russia, a U.S. official told NPR on Sunday.

The missiles, known as Army Tactical Missile System, or ATACMS, can travel about 190 miles. Their use would enable Ukrainian troops to strike Russia’s weapon stockpiles, logistical centers and airfields — which could help stop Russian forces from advancing on the battlefield and attacking Ukrainian cities.

The U.S. official, who wasn’t authorized to speak publicly about the decision, said the U.S. is allowing Ukraine to use the weapons to target in and around Kursk — the same region where some 10,000 North Korean troops were recently deployed, according to the U.S. and its allies.

The authorization marks a significant reversal in U.S. policy. Until recently, the Biden administration resisted allowing Ukraine to fire American long-range missiles into Russian territory for fear that it would only escalate the war.

The U.S. confirmed in the spring that it had sent ATACMS to Ukraine, with the caveat that the weapons would only be used inside Ukrainian territory.

British officials will likely follow suit in allowing Ukraine to use their Storm Shadow long-range missiles in Russia, the U.S. official said. These missiles can travel about 155 miles. The British needed U.S. approval because these missiles contain U.S. components.

It’s unclear how many long-range ATACMS Ukraine has but the numbers are limited since Ukraine already used some of the weapons on targets inside its territory.

A separate source on Capitol Hill, who also wasn’t authorized to speak publicly, said the decision is unlikely to be a game-changer in the war because of the limited number of such missiles and because Ukraine is already using drones to hit Russian targets.

The war has escalated since Ukrainian forces carried out a surprise incursion into Russia’s Kursk region in August. The attack was viewed as a breakthrough for Ukraine and a setback for Russia. Then, in October, North Korea sent thousands of its troops to Kursk to help Russia fight off the Ukrainian incursion.

The policy shift comes just over two months before President-elect Donald Trump will return to the White House. Trump has criticized the amount of aid given to Ukraine in its fight against Russia and claimed he could end the war in 24 hours, though he has not explained how.

NPR’s Tom Bowman contributed reporting.