Iran has used bulldozers to clear away debris at the site of Ukrainian airliner crash, potentially destroying evidence as Tehran continues to deny Western allegations that one of its own missiles downed the jet, killing all 176 people on board.

Photos from the site show at least one bulldozer clearing away wreckage and Giancarlo Fiorella of Bellingcat, a journalism website that focuses on fact-finding, said the group had verified pictures of other bulldozers at work at the scene, calling it “distressing.”

“It’s distressing, this is a potential crime scene, if this was a shoot down you don’t want to disturb the crash site before a thorough investigation has taken place,” he told the UK’s Channel 4 news. “The presence of heavy machinery, the bulldozing of the wreckage is very distressing.”

The Daily Mail also published several more pictures of bulldozers at work at the scene and said the site was now vulnerable to scavengers.

Iran on Friday denied Western allegations that one of its own missiles downed a Ukrainian jetliner that crashed outside Tehran, and called on the US and Canada to share any information they have on the crash, which killed all 176 people on board.

Western leaders said the plane appeared to have been unintentionally hit by a surface-to-air missile just hours after Iran launched around a dozen ballistic missiles at two US bases in Iraq to avenge the killing of its top general in an American airstrike last week.

The US promised “appropriate action” Friday in response to its assessment that an Iranian missile was responsible for downing a Ukrainian jetliner that crashed outside Tehran, as the Iranian government denied playing a role in the killing of all 176 people on board.

US Secretary of State Mike Pompeo became the highest-level US official to directly pin the blame on Iran, after Canadian, Australian and British leaders announced similar intelligence conclusions Thursday.

“We do believe it is likely that that plane was shot down by an Iranian missile,” he said.

Pompeo said an investigation would continue into the incident and that once it was complete he was “confident that we and the world will take appropriate action as a response.”

Iran has rejected the accusations.