A US official said Russia asked China for military equipment to use in its invasion of Ukraine, a request that heightened tensions about the ongoing war ahead of a Monday meeting in Rome between top aides for the US and Chinese governments.

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In advance of the talks, White House national security adviser Jake Sullivan bluntly warned China to avoid helping Russia evade punishment from global sanctions that have hammered the Russian economy. “We will not allow that to go forward,” he said. China in turn accused on Monday the US of spreading “disinformation.”

Chinese state broadcaster CCTV said the talks with the US were underway around 11:50 a.m. Rome time (1050 GMT), but gave no other details.

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The prospect of China offering Russia financial help is one of several concerns for President Joe Biden. A US official, speaking on condition of anonymity to discuss sensitive matters, said that in recent days, Russia had requested support from China, including military equipment, to press forward in its ongoing war with Ukraine. The official did not provide details on the scope of the request. The request was first reported by the Financial Times and The Washington Post.

The Biden administration is also accusing China of spreading Russian disinformation that could be a pretext for Russian President Vladimir Putin’s forces to attack Ukraine with chemical or biological weapons.

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Russia’s invasion of Ukraine has put China in a delicate spot with two of its biggest trading partners: the US and European Union. China needs access to those markets, yet it also has shown support for Moscow, joining with Russia in declaring a friendship with “no limits.”

In his talks with senior Chinese foreign policy adviser Yang Jiechi, Sullivan will indeed be looking for limits in what Beijing will do for Moscow.

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“I’m not going to sit here publicly and brandish threats,” he told CNN in a round of Sunday news show interviews. “But what I will tell you is we are communicating directly and privately to Beijing that there absolutely will be consequences” if China helps Russia “backfill” its losses from the sanctions.

“We will not allow that to go forward and allow there to be a lifeline to Russia from these economic sanctions from any country anywhere in the world,” he said.

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Without giving details, Chinese Foreign Ministry spokesperson Zhao Lijian said Monday that the “Ukraine situation will definitely be a hot topic” at the meeting, which had been scheduled before Russia invaded its neighbor.

Asked at a daily briefing about the reported Russian request for assistance, Zhao responded: “The US has been spreading disinformation targeting China recently over the Ukraine issue. It is malicious.”

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“What is pressing now is that all parties should exercise restraint and strive to cool down the situation, rather than fueling the tension,” Zhao told reporters. “We should promote diplomatic settlements instead of further escalating the situation.”

In a statement posted on the ministry’s website late Sunday, Zhao did not mention Ukraine, but said the sides would “exchange views on China-US relations and international and regional issues of common concern.”

The White House said the talks will focus on the direct impact of Russia’s war against Ukraine on regional and global security.

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Biden administration officials say Beijing is spreading false Russian claims that Ukraine was running chemical and biological weapons labs with US support. They say China is effectively providing cover if Russia moves ahead with a biological or chemical weapons attack on Ukrainians.

When Russia starts accusing other countries of preparing to launch biological or chemical attacks, Sullivan told NBC’s “Meet the Press,” “it’s a good tell that they may be on the cusp of doing it themselves.”

Pentagon spokesman John Kirby, on ABC’s “This Week,” said “we haven’t seen anything that indicates some sort of imminent chemical or biological attack right now, but we’re watching this very, very closely.”

The striking US accusations about Russian disinformation and Chinese complicity came after Russian Foreign Ministry spokeswoman Maria Zakharova alleged with no evidence that the US was financing Ukrainian chemical and biological weapons labs.

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The Russian claim was echoed by Chinese foreign ministry spokesman Zhao, who claimed there were 26 bio-labs and related facilities in “which the US Department of Defense has absolute control.” The United Nations has said it has received no information backing up such accusations.