Ukraine inherited alot of dangerous biological material when the old soviet union fell apart. They have that in their own labs. Around 2005, the US military went into Ukraine with the supposed mission of helping Ukraine "secure" and properly take care of all that old biological material. The US government put people in the country and built a facility in the country.
Flash forward 17 years. The US military "biological materials" mission is still ongoing in Ukraine. None of the materials Ukraine had seem to have been disposed of and nobody will give a clear answer on what the US military mission today is and that biological laboratory of theirs in Ukraine is doing.
The US government has admitted that the US military has a lab there. The US official position is that all of its various biological laboratories around the world are for "biological defense" and that that the US would never engage in biological warfare research.
The problem with that is all kinds of research that on paper is about defending against biological weapons can also be used to develop biological weapons. Its not so easy to distinguish one from the other. It becomes a very subjective question.
The mainstream in the US responded to the Russian/Chinese statements by basically repeating whatever the US military said as unquestioned truth and saying that anything said by the Russians or Chinese cannot be verified. That is just weak.
In a about a week the US went from total denial and calling everything about biolabs "conspiracy theory" to admitting that they have a lab & program in Ukraine. But disputing the Russian characterization of the work conducted at that lab in Ukraine. They have often been careful recently not to DENY what people are saying but shifting to a "you can't prove that" argument.
So the biolabs are real. But what exactly was being researched or done at the biolabs is still in dispute.