The deadly crash of a Boeing airplane in Tehran was likely caused by a technical malfunction, intelligence sources told Reuters Wednesday.

The Ukrainian International Airlines Boeing 737, en route to Kiev, crashed just hours after Iran fired missiles at bases housing U.S. forces in Iraq, leading to speculation that the plane may have been attacked.

But five intelligence sources - three Americans, one European and one Canadian - told Reuters the initial assessment of Western intelligence agencies was that the plane had suffered a technical malfunction and had not been brought down by a missile.

The Canadian source said there was evidence one of the jet’s engines had overheated.

The plane appeared to burst into a fireball shortly after takeoff, killing all 176 people on board.

Canadian Prime Minister Justin Trudeau said on Wednesday that at least 63 Canadians were on board - and that a total of 138 passengers on the flight were connecting to Canada. He also noted the timing of the tragedy.

(SOUND BITE) (ENGLISH) CANADIAN PRIME MINISTER JUSTIN TRUDEAU, SAYING:

"On behalf of all Canadians, I want to express my deepest condolences to those who are mourning the loss of a loved one. Your loss is indescribable and this is a heartbreaking tragedy. This somber day comes in the wake of deeply concerning events in Iraq. Canada condemns the missile attacks launched by Iran last night."

The crash also comes at a time of crisis for manufacturer Boeing, which has grounded its 737 MAX fleet after two crashes.

The Ukrainian Airlines plane, a 737-800, is one of the world’s most-flown models, with a good safety record, and does not have the software feature implicated in crashes of the 737 MAX.

The plane was only 3 years old, and had just been serviced January 6th.

Its black box and data recorders have been found, and investigations into the tragedy are under way.