A US official accused Moscow on Thursday of preparing to plant fake evidence to make it look like the recent mass killing of prisoners of war in an attack on a Russian-controlled prison was caused by Ukraine.
Kyiv and Moscow have traded blame over the strikes on the prison in Russian-controlled Olenivka in eastern Ukraine, which Russia said took place overnight on July 29.
White House National Security spokesman John Kirby said he believed Russian officials would doctor the scene at the prison before possible visits by outside investigators.
"Russian officials will try to frame the Ukrainian Armed Forces in anticipation of journalists and potential investigators visiting the site of the attack," Mr Kirby told reporters.
More than 50 soldiers died in the incident, including troops who had surrendered after weeks of defending the Azovstal steelworks 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 burnt bed frames but independent experts are so far unclear on what could have caused the damage.
The UN has announced a fact-finding mission, though it has not yet received final approval from Kyiv or Moscow.
President Volodymyr Zelenskyy claimed there had been “a deliberate mass murder of Ukrainian prisoners of war”.
Russia has carried out numerous attacks on civilians during its invasion of Ukraine, with evidence of summary executions and frequent aerial bombing or shelling of civilians.
In each case, Moscow has either denied committing atrocities or blamed them on Ukraine attacking its own side.
On Tuesday, Russian authorities said that prisoners held by Ukraine had been subjected to “inhuman treatment”.
- AFP contributed reporting.