With neither side showing any sign of relenting, Putin signed a decree broadening the justification for Moscow's use of nuclear weapons.

The grim anniversary opened with a Russian strike in the eastern Ukrainian region of Sumy that gutted a Soviet-era residential building and killed at least 12 people, including a child.

President Volodymyr Zelensky published images of rescue workers hauling bodies from the debris and called on Kyiv's allies to "force" the Kremlin into peace.

The foreign ministry released an anniversary statement calling on allies to ramp up military support to bring about a "sustainable" end to the war.

"Ukraine will never submit to the occupiers, and the Russian military will be punished for violating international law," the ministry said.

"We need peace through strength, not appeasement," it added, referring to growing calls for Ukraine to sit down at the negotiating table with Russia to end the war.

The Kremlin also vowed to defeat Ukraine.

"The military operation against Kyiv continues ... and will be completed," Kremlin spokesman Dmitry Peskov told reporters, using Russia's preferred language for its invasion.

- Nuclear sabre-rattling -

Washington this week said it had cleared Ukraine to use long-range Army Tactical Missile System (ATACMS) weapons against military targets inside Russia -- a long-standing Ukrainian request.

Russia's military said Ukraine used ATACMS missiles against a facility in the Bryansk region close to the border overnight.

"At 03:25 am (0025 GMT), the enemy struck a site in the Bryansk region with six ballistic missiles. According to confirmed data, US-made ATACMS tactical missiles were used," said a defence ministry statement.

Moscow has said the use of Western weapons against its internationally recognised territory would make the US a direct participant in the conflict and pledged an "appropriate and palpable response".

The strike confirmation came shortly after Putin signed a decree which enables Russia to use nuclear weapons against non-nuclear states such as Ukraine if they are supported by nuclear powers.

The new nuclear doctrine allows Moscow to unleash a nuclear response in the event of a "massive" air attack, even if it is only with conventional weapons.

Peskov said this was "necessary to bring our principles in line with the current situation."

- Deadly strike on Sumy -

Russia has stepped up strikes on Ukraine in recent days as its troops advance in the east of the country.

One overnight Russian attack hit a dormitory in the town of Glukhiv, which had a pre-war population around 30,000 people and lies just 10 kilometres (six miles) from the Kursk region in Russia, where Ukrainian troops captured territory in a major ground offensive in August.

The drone attack killed 12 people including a child, the emergency services said.

In total, Kyiv said Russia had launched 87 drones over Ukraine during the night, and that 51 were shot down.

The strike on Sumy comes just days after another Russian aerial bombardment in the border region killed 12 people and wounded 84. A separate missile strike on Monday on Odesa in southern Ukraine left 10 dead and 55 wounded.

US president-elect Donald Trump has vowed to cut US assistance to Ukraine and bring about a swift end to the war, without detailing how he would do so.

A group of European foreign ministers meeting in Warsaw on Tuesday discussed stepping up aid to Ukraine if Washington's support wanes.

"I note with appreciation the readiness of the largest European Union countries to assume the burden of military and financial support for Ukraine in the context of a possible reduction in US involvement," Polish Foreign Minister Radoslaw Sikorski said after the talks.

- 'Direct threat' to West -

Ukrainian forces have steadily lost ground in the Kursk region and have warned that Russia has mass some 50,000 troops, including North Korean forces, to wrest back the region.

The anniversary of Russia's invasion -- launched on February 24, 2022 -- comes at a perilous time for Ukrainian forces across the front, particularly near the war-battered cities of Kupiansk and Pokrovsk.

NATO chief Mark Rutte warned Tuesday that Putin must not be allowed to prevail.

"Why is this so crucial that Putin will not get his way? Because you will have an emboldened Russia on our border... and I'm absolutely convinced it will not stop there," Rutte told reporters in Brussels.

"It is then posing a direct threat to all of us in the West," he said.

The EU's outgoing top diplomat Josep Borrell also pressed member states to align with Washington in allowing Kyiv to strike inside Russia using donated long-range missiles.

"It is fully in accordance with international law," he said.