Joe Biden’s national security adviser Jake Sullivan, who is due to meet China’s top diplomat, Yang Jiechi, in Rome on Monday, warned on Sunday that Beijing will “absolutely” face consequences if it helps Moscow evade sanctions over the invasion of Ukraine.

The White House national security council declined to comment, however, on reports that Russia has asked China for military equipment since its invasion of Ukraine on 24 February.

The Financial Times, Washington Post and New York Times reported the request on Sunday, citing US officials.

Russia and China have tightened cooperation as they have come under western pressure over human rights and other issues. Beijing has not condemned Russia’s attack on Ukraine and does not call it an invasion but has urged a negotiated solution.

The Washington Post said the unidentified US officials did not state the kind of weaponry that Russia requested or how China responded.

Earlier, Sullivan told CNN the US believed China was aware Russia was planning action in Ukraine before the invasion took place, though Beijing may not have understood the full extent of what was planned.

Now, Sullivan said, Washington was watching closely to see to what extent Beijing provided economic or material support to Russia, and would impose consequences if it did.

“We are communicating directly, privately to Beijing, that there will absolutely be consequences for large-scale sanctions evasion efforts or support to Russia to backfill them,” Sullivan said. “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.”

A senior US administration official said the war in Ukraine would be a “significant topic” during Sullivan’s meeting with Yang, which is part of a broader effort by Washington and Beijing to maintain communication and manage competition between the world’s two largest economies.

“This meeting is taking place in the context of Russia’s unjustified and brutal war against Ukraine, and as China has aligned itself with Russia to advance their own vision of the world order, and so I expect … the two of them will discuss the impact of Russia’s war against Ukraine on regional and global security,” the source said.

No specific outcomes were expected from the Rome meeting, the source said, speaking on condition of anonymity.

The US on Saturday said it would rush up to $200m of additional weapons to Ukrainian forces as they try to defend against Russian shelling in the largest conflict in Europe since the second world war.

The Russian assault has trapped thousands of civilians in besieged cities and sent 2.5 million Ukrainians fleeing to neighboring countries.

The US and its allies have imposed unprecedented sanctions and banned Russian energy imports, while providing billions of dollars of military and humanitarian aid to Ukraine.

Individually and together they have appealed to China, Gulf nations and others that have failed to condemn the invasion to join in isolating Russia.

Beijing has refused to call Russia’s actions an invasion, although President Xi Jinping last week did call for “maximum restraint” after a virtual meeting with the German chancellor, Olaf Scholz, and French president, Emmanuel Macron.

Xi also expressed concern about the impact of sanctions on global finance, energy supplies, transportation and supply chains, amid growing signs that western sanctions are limiting China’s ability to buy Russian oil.

Hu Xijin, former editor-in-chief of the state-backed Chinese Global Times newspaper, said on Twitter: “If Sullivan thinks he can persuade China to participate in sanctions against Russia, he will be disappointed.“

The International Monetary Fund last week said the crisis could see China miss its 5.5% growth target this year, and its chief said she had spoken with China’s top central banker and expected mounting pressure on Russia to end the war.

While in Rome, Sullivan will also meet with Luigi Mattiolo, diplomatic adviser to the Italian prime minister, Mario Draghi, to continue coordinating the strong global response to Vladimir Putin’s “war of choice”, the source said.

The US and the Group of Seven advanced economies on Friday ratcheted up pressure on Russia by calling for revoking its “most favored nation” trade status, which would allow them to jack up tariffs on Russian goods.

Trade made up about 46% of Russia’s economy in 2020, much of that with China, its biggest export destination.