U.S. President Joe Biden on Monday warned Russia's claim that Ukraine has biological and chemical weapons is "a clear sign" Moscow is weighing the use of such armaments in its ongoing invasion of its neighbor.

Russian President Vladimir Putin's "back is against the wall and now he's talking about new false flags he's setting up, including asserting that we in America have biological as well as chemical weapons in Europe, (which is) simply not true," Biden said during a meeting with business leaders.

People who fled Ukraine because of the Russian invasion are seen at a temporary accommodation site in Korczowa, southeastern Poland, on March 14, 2022. (Kyodo) ==Kyodo

"They're also suggesting that Ukraine has biological and chemical weapons in Ukraine. That's a clear sign he's considering using both of those," he added.

Last week, Biden's National Security Adviser Jake Sullivan warned a Russian Security Council official in a phone call about the "consequences and implications" of any possible Russian decision to use chemical or biological weapons in Ukraine.

According to the United Nations, Russia said it has "evidence" of a U.S.-Ukrainian agreement to conduct biological weapons research on Ukrainian territory. But U.N. disarmament chief Izumi Nakamitsu has said the world body is not aware of any biological weapons program hosted in the East European country.

Russia invaded Ukraine on Feb. 24, an action the majority of countries around the world have criticized as an unprovoked and unjustified war.

Russia has faced stiff resistance from Ukraine, which is receiving financial and military support from the United States, Europe and other countries. Russian forces are encountering logistical problems and have made other "missteps," according to the Pentagon.

As Russia suffers from the impacts of wide-ranging economic sanctions from the United States and its allies and partners, the Biden administration warned on Monday of the potential for Moscow to conduct cyberattacks on critical infrastructure in the United States in retaliation.

Biden's deputy national security adviser for cyber issues, Anne Neuberger, acknowledged there is no evidence of any specific cyberattack that the government is bracing for, but "some preparatory activity" has been observed.