The leaders of Canada and the UK called for a full and thorough investigation into the crash, which killed all 176 people on board.
Iran has ruled out a missile strike by its air defences.
The crash came just hours after Iran carried out missile strikes on two airbases housing US forces in Iraq.
Iran is known to have Russian-made Tor missile defence systems
US media have speculated that the timing of the crash suggests the plane may have been mistaken for a US warplane as Iran prepared for possible US retaliation for the strikes.
CBS News quoted US intelligence sources as saying a satellite detected infrared “blips” of two missile launches, followed by another blip of an explosion.