KYIV, Feb 20 (Reuters) – U.S. President Joe Biden made an unannounced visit to Kyiv on Monday, promising to stand with Ukraine as long as it takes, on a trip timed to upstage the Kremlin ahead of the one-year anniversary of Russia’s invasion.

Biden, in aviator sunglasses, strode side-by-side with President Volodymyr Zelenskiy, in green battle fatigues, through central Kyiv to a gold-domed cathedral, on a bright winter morning pierced by air raid sirens.

“When Putin launched his invasion nearly one year ago, he thought Ukraine was weak and the West was divided. He thought he could outlast us. But he was dead wrong,” Biden said.

“The cost that Ukraine has had to pay is extraordinarily high. Sacrifices have been far too great … We know that there will be difficult days and weeks and years ahead.”

Outside the cathedral, burnt-out Russian tanks had been placed as a symbol of Moscow’s failed assault on the capital at the outset of its invasion, when its forces swiftly reached the city’s ramparts only to be turned back by unexpectedly fierce resistance.

Since then, tens of thousands of Ukrainian civilians and soldiers on both sides have died, cities have been reduced to rubble and millions of refugees have fled. Russia claims to have annexed nearly a fifth of Ukraine, while the West has committed tens of billions of dollars in military aid to Kyiv.

The U.S. president promised a further $500 million worth of weaponry, including artillery ammunition, anti-armour systems and air defence radars, plus tighter sanctions on Russia.

“This visit of the U.S. president to Ukraine, the first for 15 years, is the most important visit in the entire history of Ukraine-U.S. relations,” Zelenskiy said.

Foreign Minister Dmitro Kuleba called the visit a “victory of the Ukrainian people and president Zelenskiy” and a clear signal to “the swamp” – Russia – that “no one is afraid of you!”

It was clearly timed to upstage Russia’s President Vladimir Putin, due to make a major address on Tuesd