President Vladimir Putin told his Chinese counterpart Xi Jinping on Monday that Russia was open to discussing China's proposals to end the fighting in Ukraine at the start of high-stakes talks in the Kremlin.

The summit comes as China seeks to portray itself as a neutral party in the Ukraine conflict, but Washington warned the world should not be fooled by Beijing's moves.

Xi's three-day trip also serves as a show of support for internationally isolated Putin, just days after a war crimes tribunal issued a warrant for his arrest over accusation of unlawfully deporting Ukrainian children.

"We are always open to negotiations," Putin told the Chinese leader, who was on his first visit to Moscow since the start of Russia's military intervention in Ukraine last year.

The United States has accused Beijing of mulling arms exports to Moscow -- claims China has vociferously denied.

US Secretary of State Antony Blinken voiced scepticism over Xi's Ukraine proposals, warning they could be a "stalling tactic" to help Russia.

"Russia alone could end its war today. Until Russia does, we will stand united with Ukraine for as long as it takes," Blinken said later in a statement.

Xi and Putin came together in part to discuss China's 12-point position paper on the Ukraine conflict, which includes a call for dialogue and respect for all countries' territorial sovereignty.

During his initial meeting with Putin, Xi hailed "close ties" with Russia and the Russian leader said the two countries had "plenty of common objectives and tasks".

State news agency RIA Novosti said talks between the Russian and Chinese leaders lasted four and a half hours.

The two will meet again for formal talks on Tuesday.

Putin has welcomed Beijing's statements on Ukraine as being indicative of a willingness to play a "constructive role" in ending the conflict.

But Kyiv on Monday reiterated calls for Russia to withdraw its forces from Ukraine.

"We expect Beijing to use its influence on Moscow to make it put an end to the aggressive war against Ukraine," Ukrainian foreign ministry spokesman Oleg Nikolenko said in comments sent to AFP.

The head of Russia's Wagner mercenary group said Monday that his forces control more than two-thirds of the embattled eastern Ukraine town of Bakhmut -- scene of the longest battle of Russia's offensive.

"At the moment, Wagner units control around 70 percent of the city of Bakhmut and are continuing operations to complete the liberation of the city," Yevgeny Prigozhin said in an open letter to Russian Defence Minister Sergei Shoigu.

A day before Xi's arrival, a defiant Putin went to the Russian-held Ukrainian city of Mariupol -- his first visit to territory captured from Kyiv since Moscow's forces pushed across the border in February 2022.