Ukraine used U.S. ATACMS missiles to strike Russian territory for the first time on Tuesday, Moscow said, in an attack regarded by Russia as a major escalation on the war's 1,000th day.
Russia said its forces shot down five of six missiles fired at a military facility in the Bryansk region, while debris of one hit the facility, causing no casualties or damage.
Ukraine said it had struck a Russian arms depot around 110 km (70 miles) inside Russia and caused secondary explosions. It did not specify what weapons it had used.
President Joe Biden gave approval just this week for Ukraine to use the medium range U.S. missiles for such attacks, which Moscow has described as an escalation that would make Washington a direct combatant in the war and prompt retaliation.
It came amid plans for vigils to mark 1,000 days of war, with weary troops at the front, Kyiv besieged by airstrikes, and doubts about the future of Western support as Donald Trump heads back to the White House.
Military experts say U.S. missiles can help Ukraine defend a pocket it has captured as a bargaining chip inside Russia but are not likely to change the course of the 33-month-old war.
Potentially more consequential changes in the U.S. posture are expected when Trump returns to power in two months, having pledged to end the war quickly without saying how.
In an address to parliament, President Volodymyr Zelenskiy said the war's "decisive moments" would come in the next year.
"At this stage of the war, it is being decided who will prevail. Whether us over the enemy, or the enemy over us Ukrainians... and Europeans. And everyone in the world who wants to live freely and not be subject to a dictator."
A candle-lit commemoration was planned for later on Tuesday.
Thousands of Ukrainian citizens have died, over six million live as refugees abroad and the population has fallen by a quarter since Kremlin leader Vladimir Putin ordered the invasion by land, sea and air that began Europe's biggest conflict since World War Two.
Military losses have been catastrophic, although casualty figures remain closely guarded secrets. Public Western estimates based on intelligence reports say hundreds of thousands have been wounded or killed on each side.
"In the frozen trenches of the Donetsk region and in the burning steppes of the Kherson region, under shells, hail, and anti-aircraft guns, we are fighting for the right to live," Ukraine's top commander Oleksandr Syrkyi wrote on Telegram.
Tragedy has touched families in every corner of Ukraine, where military funerals are commonplace in major cities and far-flung villages, and people are exhausted by sleepless nights of air raid sirens and anguish.
In the first year after the invasion, Ukrainian troops pushed Russian forces back from the outskirts of Kyiv and recaptured swathes of territory with surprise military successes against a larger and better-armed foe.
But since then, the enemies have settled into relentless trench warfare that has ground eastern Ukrainian cities to dust. Russian forces still occupy a fifth of Ukraine and for the past year they have slowly but steadily gained ground.
The return of Trump, who has criticised the scale of U.S. aid, calls into question the united Western front against Putin, while also raising the prospect of talks to end the fighting. No such negotiations are known to have been held since the war's first months.
PROSPECT OF TALKS PROMPTS ESCALATION
A sense of escalation has been palpable as Moscow and Kyiv push to improve their battlefield positions ahead of any talks.
Already boosted by Iranian attack drones and North Korean artillery shells and ballistic missiles, Russia has now deployed 11,000 North Korean troops, some of whom Kyiv says have clashed, opens new tab with Ukrainian forces who have seized a part of Russia's Kursk region. Zelenskiy said Pyongyang could send 100,000 soldiers.
Russia continues to advance village by village in the east, claiming another Ukrainian settlement on Tuesday.
With winter setting in, Moscow on Sunday renewed its aerial assault on Ukraine's struggling power system, firing 120 missiles and 90 drones in the biggest barrage since August.
Moscow has denounced the U.S. decision to let Ukraine attack deep into its territory with missiles, saying this would make the United States a direct combatant.
Putin signed a new nuclear doctrine on Tuesday apparently intended as a warning to Washington, lowering the threshold under which Russia might use atomic weapons to include responding to attacks that threaten its territorial integrity.
TALKS, BUT ON WHAT TERMS?
Zelenskiy has said Ukraine must do its best to end the war next year through diplomatic means. But publicly there has been no narrowing of the gulf in the enemies' negotiating positions.
Kyiv has long demanded full Russian withdrawal from all occupied territory, and security guarantees from the West comparable to membership in NATO's mutual defence treaty, to prevent future Russian attacks.
The Kremlin says Ukraine must drop all ambitions to join NATO and withdraw all troops from the provinces Russia claims to have annexed since its invasion.
With a change of U.S. administration, European countries are preparing for a bigger role defending the continent.
"Moscow's escalating hybrid activities against NATO and EU countries are unprecedented in their variety and scale, creating significant security risk," the foreign ministers of Germany, France, Poland, Italy, Spain and Britain said in a joint statement on Tuesday.
