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 the streets of 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.
China, which in public has remained neutral despite signing a "no limits" friendship pact with Russia weeks before the invasion, said on Tuesday it was "deeply worried" that the Ukraine conflict could spiral out of control.
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 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.
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.
The European Union's foreign policy chief, Josep Borrell, said the bloc would approve more sanctions before the anniversary of the invasion on Feb. 24, which Russia describes as a "special military operation" to defend Russian sovereignty.
China's top diplomat Wang Yi on Monday called for a negotiated settlement to the Ukraine war during a stopover in Hungary ahead of a visit to Moscow for talks. Ukraine says any diplomatic solution requires the withdrawal of Russian forces from its territory.
"China is deeply worried that the Ukraine conflict will continue to escalate or even spiral out of control," China's foreign minister Qin Gang said on Tuesday in a speech at a forum held at the foreign ministry.
"We urge certain countries to immediately stop fuelling the fire," he said in comments that appeared to be directed at the United States, adding that they must "stop hyping up 'today Ukraine, tomorrow Taiwan'".
Russia is trying to secure full control of two eastern provinces forming Ukraine's Donbas industrial region. It 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 trumpet a year after he launched Europe's biggest conflict since World War Two.
Ukraine expects to receive large supplies of Western weaponry in coming months that will help it mount a planned counteroffensive. In recent weeks, Ukrainian forces claimed to have inflicted huge casualties while repelling attacking Russian forces.