His comments follow a similar message by Canadian Prime Minister Justin Trudeau.

"There is now a body of information that the flight was shot down by an Iranian Surface to Air Missile. This may well have been unintentional," Johnson said in a statement on the air disaster in which four British passengers died.

Johnson reiterated the call for "all sides urgently to de-escalate to reduce tensions in the region."

The Ukraine International Airlines (UIA) Boeing 737NG went down 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.

"We are working closely with Canada and our international partners and there now needs to be a full, transparent investigation," into the plane crash, Johnson added.

The British PM also called for "an immediate and respectful repatriation of those who've lost their lives to allow their families to grieve properly".

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