President Biden’s national security adviser met with a top Chinese official on Monday to warn against China giving Russia military or economic assistance, as the Kremlin struggles with the aftermath of its invasion of Ukraine.

With its armed forces experiencing unexpected difficulties in Ukraine and its economy badly damaged by international sanctions, Russia has requested aid from China, U.S. officials said this weekend. Financial analysts have said that Russia could default on its debts this week.

The national security adviser, Jake Sullivan, met in Rome for seven hours with Yang Jiechi, a member of the Communist Party’s Politburo and director of the party’s foreign affairs commission. The White House is trying to peel away one of the few potential allies President Vladimir V. Putin of Russia has as his forces step up their assault on Kyiv and other Ukrainian cities.

“We have been very clear both privately with Beijing and publicly with Beijing that there would be consequences for such support,” Ned Price, the State Department spokesman, said at a press briefing in Washington, in response to questions about the Rome meeting.

The meeting took place in part “to precisely make clear our concerns,” he said, adding, “We will ensure that no country is able to get away with such a thing.”

Similarly, Jen Psaki, the White House press secretary, said, “Support of any kind, there would be consequences for that.” Neither she nor Mr. Price elaborated on those consequences.

Administration officials have not said how China has responded to the Russian request, or whether any aid had been offered or delivered.

While Monday’s meeting was scheduled long before Russia’s Feb. 24 invasion of Ukraine, it took place right after American officials revealed that they had obtained intelligence that Russia asked for military help in its bogged-down invasion, perhaps including Chinese-made drones and intelligence support.

China has said nothing about receiving such requests from Russia, but the two countries have drawn closer recently, united by having a common adversary in United States.