The White House continued to push back on allegations from Russia that the US has biowarfare labs in Ukraine, maintaining on Thursday that it is Moscow that has a biological weapons program.

Spokeswoman Jen Psaki said not only does Russia have the "capacity" to use chemical and biological weapons but it also has a "history of using" them.

"In this moment we should have our eyes open for that possibility," she told reporters.

The warning comes in response to claims by Russian Foreign Ministry spokeswoman Maria Zakharova who said that documents suggest "components of bioweapons were being developed in Ukraine."

Speaking at a weekly briefing in Moscow, Zakharova said the Russian Armed Forces received evidence of the development of biological weapon components by Ukraine under US guidance from employees of Ukraine's biological labs.

Psaki on Wednesday took to Twitter to dismiss the suggestions, saying that the US is in full compliance with its obligations under the Chemical Weapons Convention and the Biological Weapons Convention, adding Washington "does not develop or possess such weapons anywhere."

"It’s Russia that has long maintained a biological weapons program in violation of international law," she said.

Psaki demurred when asked by reporters if a potential use of chemical weapons by Russia in Ukraine would result in a US military response, saying US President Joe Biden does not intend to send the "US military to fight in Ukraine against Russia."

Russia's war on Ukraine, which began on Feb. 24, has drawn international condemnation, led to financial sanctions on Moscow and spurred an exodus of global companies from Russia.

At least 516 civilians have been killed and 908 others injured in Ukraine, according to UN figures, with the real toll feared to be higher.

More than 2.1 million people have fled Ukraine to neighboring countries, according to the UN refugee agency./aa