Russia on Wednesday sought the explanation of the United States about a military biological programme in Ukraine, claimed by Moscow.
However, Washington has already dismissed the allegation as "absurd" misinformation, reports Reuters.
Russian foreign ministry spokeswoman Maria Zakharova said evidence of the alleged programme had been uncovered by Russia during what it calls its military operation in Ukraine, which its forces invaded on Feb 24. It involved deadly pathogens including plague and anthrax, she said.
A Ukrainian presidential spokesperson said: "Ukraine strictly denies any such allegation".
In response to earlier Russian allegations about the purported military biological programme in Ukraine, a Pentagon spokesman said on Tuesday: "This absurd Russian misinformation is patently false".
Zakharova said Russia had documents showing that the Ukrainian health ministry had ordered the destruction of samples of plague, cholera, anthrax and other pathogens after Feb 24.
"We can already conclude that in Ukrainian biological laboratories in direct proximity to the territory of our country, development of components of biological weapons was being carried out," she said.
It was not possible to independently confirm the authenticity of any such documents.
Zakharova said the alleged programme was financed by the Pentagon. "We are not talking here about peaceful uses or scientific goals."
The Biden administration must officially explain to the world "officially, not through talking heads" about the programmes in Ukraine, she said, adding: "We demand details."
Zakharova said it was not clear if the alleged materials had been destroyed and she asked if they had fallen into the hands of extremists or nationalists.
Russia has made allegations about the United States working with Ukrainian laboratories to develop biological weapons for several years, accusations that increased in the wake of the coronavirus pandemic. Both countries have consistently denied the reports.
Since the 1990s, the two countries have worked together as part of an international agreement aiming to reduce the threat of weapons of mass destruction following the fall of the Soviet Union.
Since 2005, they have also collaborated on preventing outbreaks of infectious diseases, including on vaccine research.
In addition, there are public health labs in Ukraine, as in most countries of the world, that research other dangerous diseases affecting both animals and humans to better understand how to mitigate those threats.