Kyiv, Ukraine - Ukraine's leader Volodymyr Zelensky hailed his country's "resistance" and "heroism" on Monday – the third anniversary of Russia's invasion – as European leaders arrived in Kyiv in a show of solidarity.

Russian President Vladimir Putin's decision to launch what he called a "special military operation" set off the biggest conflict in Europe since World War II.

Tens of thousands of soldiers – from both sides – and Ukrainian civilians have been killed, cities across the country's south and east have been flattened, and millions forced to flee their homes.

Now, three years after the West rallied behind Ukraine and Zelensky, Trump's return to the White House has threatened a massive shift in US policy toward Ukraine.

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As Russian troops are still advancing across the east, Zelensky on Monday hailed "three years of resistance. Three years of gratitude. Three years of absolute heroism of Ukrainians," adding: "I thank everyone who defends and supports it."

Arriving in Kyiv by train, EU Commission chief Ursula von der Leyen said Ukraine was fighting "for survival" and that Europe's "destiny" was at stake in Ukraine.

"We are in Kyiv today, because Ukraine is Europe. In this fight for survival, it is not only the destiny of Ukraine that is at stake. It's Europe's destiny," she said in a post on X.

Brussels on Monday hit Russia with a new round of sanctions targeting not only "the Russian shadow fleet but those who support the operation of unsafe oil tankers, videogame controllers used to pilot drones, banks used to circumvent our sanctions, and propaganda outlets used to spout lies," the European Union's top diplomat Kaja Kallas said.

In an apparent rebuke of Trump's moves to sideline Kyiv from talks on how to end the war, EU Council President Antonio Costa said: "In Ukraine, about Ukraine, with Ukraine."

The presidents or prime ministers of Canada, Denmark, Estonia, Finland, Iceland, Latvia, Lithuania, Norway, Spain, and Sweden had all arrived in Kyiv on Monday morning, according to their posts on social media and Ukraine's Suspilne public broadcaster.

Zelensky said 13 leaders would be in Kyiv on Monday with another 24 joining a special meeting online.

The Ukrainian leader said he hoped it would be a "turning point." He is calling for security guarantees from Kyiv's backers to ensure Russia does not use any ceasefire to rearm and attack again at a later date.

On Sunday, Zelensky offered to resign if it meant Ukraine could be given NATO membership.

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The Kremlin on the eve of the anniversary repeated Russia's position that it would not give up territory it has captured in Ukraine's east and south. Moscow has also said it would not accept Ukrainian admission to NATO.

Trump is pushing both Ukraine and Russia for a swift end to the war.

Triggering alarm in Kyiv and across Europe, Trump has restarted diplomacy with Moscow, calling Putin for a 90-minute phone conversation and dispatching Secretary of State Marco Rubio to Saudi Arabia for a meeting with Russian Foreign Minister Sergei Lavrov.

On the battlefield, Russian troops have been advancing while on Monday Ukraine claimed to have hit a Russian oil refinery southeast of Moscow in its latest drone attack deep behind the front line.

French President Emmanuel Macron was due in Washington later Monday for a meeting with Trump.

Macron said he plans to tell the Republican: "You cannot be weak in the face of President Putin."

Europe has been left scrambling to respond as Trump and his team have not only questioned support for Ukraine, but also decades of transatlantic military cooperation between the US and its European allies.

Ukrainian soldiers in the east told AFP they were nervous about Trump's bid for a swift ceasefire.

"It scares me more. Because the bloodiest moments always come before a truce," said Andrii, a 25-year-old serving with Ukraine's army in the east.

"In this war, you don't count days, weeks, numbers, or any dates," said Mykola, a 38 year-old gun commander stationed in the eastern Donetsk region.

"I don't want to give up Ukrainian lands ... we've been fighting for so long," he told AFP on the eve of the anniversary. "But everyone is tired of the war."