KYIV, Ukraine — Ukraine fired several American-supplied longer-range missiles into Russia, officials said Tuesday, marking the first time Kyiv used the weapons that way in 1,000 days of war.

The use of the Army Tactical Missile System, known as ATACMS, came as Russian President Vladimir Putin formally lowered the threshold for using nuclear weapons, opening the door to a potential nuclear response by Moscow to even a conventional attack by any nation supported by a nuclear power. That could include Ukrainian attacks backed by the U.S.

A Telegram channel affiliated with the Ukrainian military posted a video Tuesday that it says shows U.S.-supplied ATACMS missiles being fired from an undisclosed location in Ukraine. The Associated Press could not independently verify the date and location the video was filmed.

According to a U.S. official, Ukraine fired about eight of the missiles, and just two were intercepted by the Russians. The official said that the U.S. was still assessing battle damage, but that the missiles struck an ammunition supply location in Karachev, a city of about 18,000 people in Russia’s Bryansk region. The official spoke on the condition of anonymity to discuss intelligence assessments.

The developments marked a worrying escalation in the conflict that has repeatedly ratcheted up international tensions. U.S. officials recently expressed dismay at Russia’s deployment of North Korean troops to help it fight Ukraine, while Moscow seethed when Washington eased restrictions on the ATACMS in recent days.

The 1,000-day mark has magnified scrutiny of how the war is unfolding and how it might end, amid signs that a turning point may be coming with U.S. President-elect Donald Trump entering the White House in about two months’ time. Trump has pledged to swiftly end the war and has criticized the amount the U.S. has spent on supporting Ukraine.

Neither Russia nor Ukraine can sustain the war for a long time, analysts say, though Russia would be able to keep going for longer due to its vaster resources.

Ukraine’s forces are under severe Russian pressure on the battlefield at places on the about 600-mile front line where its army is stretched thin. Ukrainian civilians, meanwhile, have repeatedly been attacked by Russian drones and missiles.

Ukraine claimed Tuesday that it hit a military weapons depot in Russia’s Bryansk region overnight, though it didn’t specify what weapons it used. The Ukrainian General Staff said multiple explosions and detonations were heard in the targeted area around Karachev.

Asked at a news conference if Ukraine had struck the Bryansk region ammunition depot with ATACMS, Ukraine’s President Volodymyr Zelenskyy declined to provide any details. However, he said, “Ukraine has long-range capabilities, including domestically produced long-range drones … and now we have ATACMS as well.”

In a statement carried by Russian news agencies, the Russian Defense Ministry said the military shot down five ATACMS missiles and damaged one more. The fragments fell on the territory of an unspecified military facility and sparked a fire, but didn’t cause any damage or casualties, it said.

Neither side’s claims could be independently verified.

Ukraine in the course of the war has been able to reach much deeper into the vast country — but with drones rather than missiles. For instance, Russian officials have reported intercepting Ukrainian drones over Moscow, which is about 310 miles from the border and most recently Izhevsk, a city about 900 miles from the frontier.

Earlier on Tuesday, Ukrainian officials reported a third Russian strike in as many days on a residential area in Ukraine killed at least 12 people, including a child.