KYIV--Russian President Vladimir Putin was due to make a speech on Tuesday setting out aims for the second year of his invasion of Ukraine, a day after U.S. President Joe Biden walked central Kyiv promising to stand with Ukraine as long as it takes.

Following his surprise visit to Kyiv, Biden flew to Poland and on Tuesday will give a speech on how the United States has helped rally the world to support Ukraine and stress American support for NATO’s eastern flank.

Biden, in his trademark aviator sunglasses, and President Volodymyr Zelenskiy, in green battle fatigues, walked side-by-side to a gold-domed cathedral in Kyiv on a bright winter Monday morning pierced by the sound of air raid sirens.

“When (Russian President Vladimir) 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, burned-out Russian tanks stand as a symbol of Moscow’s failed assault on the capital at the outset of its invasion, which began on Feb. 24. Its forces swiftly reached Kyiv’s ramparts--only to be turned back by unexpectedly fierce resistance.

Since then, Russia’s war has killed tens of thousands of Ukrainian civilians and soldiers on both sides, cities have been reduced to rubble, and millions of refugees have fled. Russia says it has annexed nearly a fifth of Ukraine, while the West has pledged tens of billions of dollars in military aid to Kyiv.

“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.

Biden traveled to Ukraine’s capital by overnight train from Poland, arriving after roughly 10 hours at 8 a.m. on Monday, before returning there the same way, leaving just after 1 p.m. (1100 GMT), according to a White House pool report by a Wall Street Journal reporter.

Biden arrived late on Monday in Warsaw, where he is scheduled to meet Poland’s President Andrzej Duda, along with other leaders of countries on NATO’s eastern flank, the following day.

While Biden was in Kyiv, the State Department announced a further $460 million in U.S. aid to Ukraine, including $450 million worth of artillery ammunition, anti-armor systems and air defense radars, and $10 million for energy infrastructure.

The European Union’s foreign policy chief, Josep Borrell, said the bloc would approve more sanctions before the anniversary of the conflict, which Russia says is a “special military operation” to defend Russian sovereignty.

Russia was notified before Biden’s departure, officials in Washington and Moscow said, apparently to avoid the risk of an attack on Kyiv while he was there.

“Of course for the Kremlin this will be seen as further proof that the United States has bet on Russia’s strategic defeat in the war and that the war itself has turned irrevocably into a war between Russia and the West,” said Tatiana Stanovaya, a Russian political analyst.

Putin will update Russia’s political and military elite on the Ukraine conflict, the biggest confrontation with the West since the depths of the Cold War, in a speech to members of both houses of parliament on Tuesday.

He will also give his analysis of the international situation and outline his vision of Russia’s development after the West imposed sweeping sanctions on it, the Kremlin said.

The speech is due to begin at 0900 GMT in central Moscow.

WINTER OFFENSIVE

Russia has sent thousands of conscripts into Ukraine for a winter offensive but has secured only scant gains so far in assaults in frozen trenches up and down the eastern front in recent weeks.

Kyiv and the West see it as a push to give Putin victories to tout a year after he launched Europe’s biggest conflict since World War Two.

Moscow received its own signal of diplomatic support on Monday, with China’s top diplomat Wang Yi expected for talks. In public, China has remained neutral over the conflict despite signing a “no limits” friendship pact with Russia weeks before the invasion.

Washington has said in recent days it is concerned Beijing could begin supplying Moscow with arms. Chinese Foreign Ministry spokesperson Wang Wenbin said the United States was “in no position to make demands of China.”

Wang Yi on Monday called for a negotiated settlement to the Ukraine war during a stopover in Hungary ahead of a visit to Moscow.

Ukraine says any diplomatic solution requires the withdrawal of Russian forces from its territory.

Russia is trying to secure full control of two eastern provinces forming Ukraine’s Donbas industrial region.

Kyiv, which is absorbing a major influx of Western weaponry in the coming months for a planned counteroffensive, has lately stuck mainly to defense on the battlefield, claiming to be inflicting huge casualties on the assaulting Russian forces.

Britain’s Ministry of Defense said Russia’s casualties included two elite brigades of thousands of marines probably rendered “combat ineffective” by losses sustained in failed attempts to storm Vuhledar.

“The Russian forces are likely under increasing political pressure as the anniversary of the invasion draws near,” it said, predicting Moscow may claim to have captured Bakhmut regardless of the situation on the ground.

“If Russia’s spring offensive fails to achieve anything, then tensions within the Russian leadership will likely increase.”