US President Joe Biden was due to meet eastern European leaders on Wednesday to discuss support for Ukraine, while President Vladimir Putin held talks with China's top diplomat in Moscow.
Wang Yi's visit comes after Washington and NATO voiced concern that China could be preparing to supply Russia with weapons to pursue its war in Ukraine.
Biden on a visit to Poland on Tuesday said Ukraine would "never be a victory for Russia", while Putin vowed to press on with the nearly year-long war.
In a state of the nation address, Putin also accused the West of escalating the conflict and announced Moscow would suspend participation in the New START nuclear arms treaty with Washington.
The Russian president said increasingly stringent sanctions would fail and vowed his country would keep fighting to "systematically" achieve its war aims.
Speaking hours later in the capital of NATO ally Poland in front of a flag-waving crowd outside Warsaw's Royal Castle, Biden said the West was "not plotting to attack Russia as Putin said".
The 80-year-old leader had a day earlier made a surprise visit to Kyiv, his first since the invasion began and just days before the war's one-year anniversary.
"There should be no doubt: our support for Ukraine will not waver, NATO will not be divided, and we will not tire," he said.
Later Wednesday, Biden is due to meet leaders of countries on NATO's eastern flank which have led calls for military assistance to Ukraine and where there is widespread concern that the conflict could spill over.
'Unwavering support'
The White House said Biden would "reaffirm the United States' unwavering support for the security of the alliance".
Meanwhile in Moscow, Putin met Wang Yi, who is on the last stop of a European tour during which he met Ukraine's Foreign Minister Dmytro Kuleba.
Beijing has sought to position itself as a neutral party, while maintaining close ties with strategic ally Russia.
It has said it is "deeply concerned" and that the conflict is "intensifying and even getting out of control".
China has promised to publish a proposed "political solution" to the Ukraine conflict this week.
At the start of the meeting, Putin said cooperation between Russia and China was "very important to stabilise the international situation".
Putin's decision to suspend participation in New START was met with widespread international condemnation, though Russia's foreign ministry later said Moscow would continue to comply with the treaty's restrictions in a "responsible approach".
The 2010 deal is the last remaining nuclear arms control treaty between the world's two main nuclear powers.
US Secretary of State Antony Blinken said Russia's decision was "deeply unfortunate and irresponsible" but that Washington was still willing to talk about the issue.
NATO Secretary General Jens Stoltenberg said the move meant that "the whole arms control architecture has been dismantled".
‘We'll make them'
When the Kremlin launched its Ukraine offensive, the so-called "special military operation" was planned to be a rapid conquest leading to capitulation and the installation of a pro-Russian regime.
Since then, Russia has been forced to give up ground but has kept up a barrage of drone and missile attacks, while the military and civilian toll has spiralled.
Various Western sources estimate the conflict has caused 150,000 casualties on each side.
Moscow's relentless struggle to capture the city of Bakhmut has also exposed tensions between the Russian military and the Wagner mercenary group.
The private fighting force's head, Yevgeny Prigozhin, on Tuesday accused military chiefs of refusing to sufficiently supply his group, saying this amounted to "treason".
Russia's defence ministry responded by detailing ammunition deliveries and denouncing "absolutely false" reports of shortages.
Prigozhin on Wednesday responded by asking ordinary Russians to put pressure on the army to give his fighters ammunition.
"We'll make them give (us) ammunition," he said on Telegram.
