The initial assessment of Western intelligence agencies is that a Ukrainian airliner which crashed in Iran on Wednesday was not brought down by a missile, said a Canadian security source.

The source, who declined to be identified, said the agencies believed the Boeing (BA.N) 737 plane had suffered a technical malfunction.

The disaster occurred shortly after Iran launched a series of missile attacks against two military bases in Iraq that housed US troops.

“The initial assessment of Western intelligence agencies is that the plane was not brought down by a missile. There is no evidence to suggest that,” said the source.

The agencies believe the most likely cause of the crash was a malfunction, the source added, saying there was some evidence one of the plane’s engines had overheated.

Boeing said it had no additional comment. Earlier, the company said it was in contact with the airline and was ready to assist.

In July 2014 a Malaysia Airlines flight from Amsterdam to Kuala Lumpur was shot out of the sky over eastern Ukraine during a rebellion by Russian-backed separatists, killing all 298 people on board.