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Senior US and Chinese officials held a long meeting in Rome on Monday, with the US expressing "deep concerns" during "intense" discussions on Russia's war in Ukraine and other security matters.
US National Security Adviser Jake Sullivan “raised a range of issues in US-China relations” with Beijing’s top diplomat, Communist Party Politburo member Yang Jiechi, the White House said.
The seven-hour meeting, the most senior this year between the two powers, featured "substantial discussion of Russia’s war against Ukraine" and "underscored the importance of maintaining open lines of communication between the United States and China", the White House said.
A senior US official described the Rome talks as "intense".
The meeting was a "timely and important conversation in this crisis moment", the official said, noting that the US continues to "have deep concerns about China's alignment with Russia".
Moscow and Beijing have drawn closer in what Washington sees as an increasingly hostile alliance of the authoritarian nuclear powers.
Mr Sullivan's meeting was planned weeks ago, officials said, but it took on new urgency after Russian President Vladimir Putin's attacks on Ukrainian cities.
US media earlier reported that Russia has asked China for military and economic assistance as its troops struggle to make ground in Ukraine and its economy faces devastation from western sanctions.
Chinese Foreign Ministry spokesman Zhao Lijian on Monday rejected the accusations, calling them “malicious".
“The top priority now is that all parties should exercise restraint to de-escalate and cool down the situation instead of fuelling the tensions,” Mr Zhao said.
The New York Times quoted a US official who said that Moscow also asked Beijing for economic assistance, but there were no details on the request or whether China had responded.
The senior US official declined to comment on whether China is open to providing Russia with military support.
"We are communicating directly and privately to China about our concerns about the kinds of support the other countries might be providing to Russia," the official said.
Mr Sullivan, the official said, "was direct about those concerns and the potential implications and consequences of certain actions".
The two sides also discussed North Korea and Taiwan.
US President Joe Biden's administration has sought to persuade Beijing to use its influence in Moscow to help end the Ukraine war, which is now in its third week.
Mr Biden's top advisers have pressured China to enforce sanctions on Russia’s economy, which were imposed by the US and its European and Asian allies.
US Treasury Secretary Janet Yellen last week said the sanctions were limiting China's ability to buy Russian oil, and Beijing was not “meaningfully offsetting or lessening” sanctions pressure on Moscow.
“My sense is that financial institutions in China that do business in dollars and in euros are worried about the impact of sanctions,” Ms Yellen said.
CIA Director William Burns told the Senate intelligence committee that Beijing was "unsettled" by the war and had not foreseen that Russian forces would struggle in Ukraine.
China’s President Xi Jinping "in particular is unsettled by what he's seeing, partly because his own intelligence doesn't appear to have told him what was going to happen", Mr Burns said.
China abstained from a key vote at the UN Security Council regarding the war.
The Biden administration saw the abstention as an encouraging sign of Beijing creating distance from Russia on the international stage.
Agencies contributed to this report