Ukraine has used US ATACMS missiles to strike Russian territory for the first time, officials in Moscow say, in a major escalation on the war's 1000th day.
Russia said its forces shot down five of six missiles fired at a military facility in the western Bryansk region while debris of one hit the facility, causing no casualties or damage.
Ukraine said it had struck a Russian arms depot about 110km inside Russia and caused secondary explosions.
It did not specify what weapons it had used.
US President Joe Biden gave approval just this week for Ukraine to use the medium range US missiles for such attacks, which Russia has described as an escalation that would make the United States a direct combatant in the war and prompt retaliation.
President Vladimir Putin on Tuesday approved an updated nuclear doctrine lowering the threshold that would prompt Russia to consider using nuclear weapons.
The new policy says any conventional assault on Russia by a non-nuclear power supported by a nuclear power will be considered to be a joint attack.
Any mass aerospace attack with aircraft, cruise missiles and unmanned aircraft that crossed Russia's borders could also trigger a nuclear response, it says.
It came amid plans for vigils to mark 1000 days of war, with weary troops at the front, Kyiv besieged by air strikes and doubts about the future of foreign support as Donald Trump heads back to the White House.
Military experts say US missiles can help Ukraine retain a pocket it has captured inside Russia - in the Kurk region - as a bargaining chip but are not likely to change the course of the 33-month-old war.
The Bryansk region, where the Russian military arsenal was targeted by Ukrainian forces, lies north of Kursk.
Potentially more consequential changes in the US 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, Ukrainian 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."
Zelenskiy set out what he called a "resilience plan" for the country as a domestic foil to the "victory plan" he pitched to allies earlier, and said it was needed to force Russia to negotiate an end to the war in good faith.
Although he said the full details of the plan would be disclosed later in the year, it comprises steps to stabilise the front line, support military innovation and arms production as well as measures to shore up unity and cultural identity.
"Unity is the first point of our internal resilience plan," he said.
Zelenskiy said Ukraine would produce at least 30,000 long-range drones next year, a weapons system that the country's forces have used to narrow the gap in strike capabilities with Russia and to strike targets deep inside its much larger eastern neighbour.
A candle-lit commemoration was planned for later on Tuesday.
Thousands of Ukrainian citizens have died, more than six million live as refugees abroad and the population has fallen by a quarter since Putin ordered the invasion by land, sea and air.
with EFE
