“We expect that Russian officials are planning to falsify evidence in order to attribute the attack on the Olenivka prison on the 29th of July,” said White House spokesman John Kirby.
“We anticipate that Russian officials will try to frame Ukrainian armed forces in anticipation of journalists and potential investigators visiting the site of the attack,” Kirby told reporters.
Kirby cited undisclosed US intelligence reports in making the claim.
But he said the United States expects that Moscow will try to pin the blame on a US-supplied Himars precision-guided missile, using “planted evidence” of fragments of such missiles allegedly found at the site.
Claims to that extent are already appearing in the media, Kirby said.
More than 50 soldiers died in the incident, including troops who had surrendered after weeks of defending the Azovstal steel works in Mariupol.
Russia has claimed that Ukraine carried out a strike on its own captured fighters, while Ukrainian authorities accuse Russia of covering up a deliberate massacre.
Russian television images showed a charred room crammed with burned bed frames but independent experts are so far unclear on what could have caused the damage visible.
Ukraine’s President Volodymyr Zelensky called it “a deliberate mass murder of Ukrainian prisoners of war.”
The United Nations has announced a fact-finding mission, though it has not yet received final approval from Kyiv or Moscow.
The International Committee of the Red Cross said it had requested access to the site immediately after learning of the alleged attack on 29 July.
But on Wednesday the ICRC said it had not yet received access to understand the fate of the Ukrainian prisoners of war.
“As of yet, we have not been granted access to the PoWs affected by the attack nor do we have security guarantees to carry out this visit,” the organisation said.
“We will keep requesting access to PoWs who are or were held in Olenivka, and any other sites where PoWs are held, guided by our humanitarian commitment and our mandate under the Geneva Conventions.”