Iran denies missile downed Ukrainian plane

Iran's civil aviation chief denied Friday that a missile downed a Ukrainian airliner which crashed killing all 176 on board, dismissing claims of a catastrophic mistake by Tehran's air defences.

The declaration came as Tehran faced mounting international pressure to allow a "credible" investigation into the crash, which Britain and Canada suggested was caused by an accidental missile strike.

"One thing is for certain, this airplane was not hit by a missile," Iran's civil aviation chief Ali Abedzadeh said.

The Boeing 737 crashed on Wednesday shortly after Tehran launched missiles at US forces in Iraq in response to the killing of a top Iranian general in a US drone strike in Baghdad.

It is Iran's worst civil aviation disaster since 1988 when the US military said it shot down an Iran Air plane over the Gulf by mistake, killing all 290 people on board.

The majority of the passengers on Ukraine International Airlines Flight PS752 were dual national Iranian-Canadians but they also included Ukrainians, Afghans, Britons and Swedes.

Canadian Prime Minister Justin Trudeau said Thursday that multiple intelligence sources indicated that an Iranian surface-to-air missile downed the plane after it took off from Tehran.

"We know this may have been unintentional. Canadians have questions, and they deserve answers," Trudeau told reporters.

But Abedzadeh rejected the allegation, saying that "any remarks made before the data is extracted (from the plane's black box flight recorders)...is not an expert opinion."