US, British and Canadian authorities now all believe a passenger plane that crashed in Iran was shot down by a missile.

A total of 176 people, 63 of them Canadian nationals, died when the Ukrainian International Airlines plane went down shortly after take-off.

Canadian president Justin Trudeau has called for a thorough investigation.

“This may well have been unintentional,” he said, echoing the thoughts of most experts and world leaders.

Aaron David Miller, a prominent US diplomacy expert who has worked for both Republican and Democratic administrations, told Kate and Quarters on 3AW Breakfast it would not be surprising to learn Iran had accidentally shot the plane thinking it was an enemy aircraft.

“It happens because you’ve got aggressive, nervous and, in this case, incompetent Iranian intel and radar acquiring heat signals of what was clearly a commercial airliner,” Mr Miller said.

“They acted, obviously, before doing what they needed to do to validate the reality that this aircraft had no hostile intent.

“The political ramifications I find fascinating.

“It really does undermine what the Iranian regime wanted to portray as a moment of great national honor, retaliation for the targeted killing of Qassem Soleimani.”

Click PLAY to hear his full comments

(Photo by Rouhollah Vahdati/ISNA/AFP via Getty Images)