More than 20 foreign leaders are in Russia to attend a vast military parade on Friday marking 80 years since the defeat of Nazi Germany in World War II, taking place three years into Russia's offensive in Ukraine.

Putin ordered troops into Ukraine in February 2022 and has marshalled the memory of Soviet victory against Nazi Germany to justify his campaign and rally society behind the offensive, which has killed tens of thousands of people.

In a meeting in the Kremlin, Putin told Xi: "Together with our Chinese friends, we firmly stand on guard of historical truth, protect the memory of events of the war years and counter modern manifestations of neo-Nazism and militarism."

Russian society has seen unprecedented militarisation during the Ukraine conflict and the Kremlin has tightly controlled the memory of World War II.

Putin claimed that his offensive against Ukraine is aimed at "de-Nazifying" the country, which Kyiv called "incomprehensible".

Russia has captured swathes of Ukrainian territory and flattened cities and towns across the east with daily bombardments, forcing millions to flee their homes.

Xi told Putin that Beijing stood alongside Russia in the face of "hegemonic bullying" -- a nod to the two countries' anti-US stance.

"In the face of the international counter-current of unilateralism and hegemonic bullying behaviour, China will work with Russia to shoulder the special responsibilities of major world powers," Xi said.

Ahead of the meeting, Putin called Xi his "dear friend", while Xi referred to the Kremlin leader as his "old friend".

- Truce -

Putin has ordered his army to stop firing on Ukraine for three days to mark the May 9 celebrations -- an order that came into effect at midnight (2100 GMT Wednesday).

But Ukraine, which dismissed the ceasefire as theatrics and never said it would abide by it, said Russia had broken its own order after just a few hours.

Ukrainian authorities said Moscow launched an aerial bomb attack on the northeastern Sumy region overnight.

"During the night, the enemy intensified tactical aviation strikes using guided aerial bombs in the Sumy region," Kyiv's air force said.

However, it said that as of 8:00 am, "no missile attacks or attack drones were recorded in Ukrainian airspace."

Ukrainian President Volodymyr Zelensky repeated his call for an unconditional 30-day full ceasefire -- a US proposal he previously accepted but that was rejected by Putin.

Zelensky denounced Moscow's World War II commemorations as a "parade of cynicism" and renewed calls for support against Russia.

"Just as it did 80 years ago, when it finally became clear to everyone: evil cannot be appeased. It must be fought. Together. Resolutely. With force. With pressure," he said on social media.

Ukrainian drone attacks have caused travel chaos across Russia this week, shutting dozens of airports and forcing hundreds of flights to be cancelled or rerouted.

US President Donald Trump has sought to end Moscow's assault on Ukraine since his inauguration in January, but has failed to ease hostilities between the enemies.

The White House has become increasingly frustrated at the lack of progress and Vice President JD Vance on Wednesday called on the two sides to enter direct talks.

- Parade -

The Kremlin was forced Wednesday to say it was taking "all necessary measures" to ensure the safety of world leaders in Russia for the parade.

In the run-up to the event, Putin has railed against what he casts as a distortion of Russia's World War II history -- criticising what he sees in the West as an attempt to downplay the Soviet Union's contribution.

"The countless sacrifices made by both our peoples are worth remembering forever. The Soviet Union gave 27 million lives, laying them on the altar of the Fatherland and on the altar of victory," he told Xi.

Trump has in recent days hailed the United States' contribution as the most decisive in the allies' 1945 victory over Nazi Germany.

World War II is officially remembered in Russia as the "Great Patriotic War", beginning with Germany's surprise invasion of the Soviet Union in 1941 and ending with Germany's capitulation in 1945.

The period between 1939 and 1941 -- when the Soviet Union had a non-aggression pact with Nazi Germany and invaded Poland -- is glossed over in official history books.