WASHINGTON — It is “highly likely” that Iran shot down the civilian Ukrainian jetliner that crashed near Tehran late Tuesday, killing all 176 people on board, declared U.S., Canadian and British officials Thursday. They said the fiery missile strike could well have been a mistake amid rocket launches and high tension throughout the region.

The crash came just a few hours after Iran launched a ballistic attack against Iraqi military bases housing U.S. troops in its violent confrontation with Washington over the U.S. drone strike that killed an Iranian Revolutionary Guard general. The airliner could have been mistaken for a threat, said four U.S. officials, speaking on condition of anonymity to discuss sensitive intelligence.

Canadian Prime Minister Justin Trudeau, whose country lost at least 63 citizens in the downing, said in Ottawa: “We have intelligence from multiple sources including our allies and our own intelligence. The evidence indicates that the plane was shot down by an Iranian surface-to-air missile.”

U.K. Prime Minister Boris Johnson and Australian Prime Minister Scott Morrison gave similar statements.

It was not immediately clear how the U.S. and its allies would react. U.S. troops were on high-alert.