U.S. Treasury Secretary Steven Mnuchin said the U.S. will issue waivers on sanctions against Iran to allow investigators from the U.S. and other countries to participate in the probe of a Ukrainian jetliner crash in Tehran earlier this week.

The investigation into a Boeing Co,. 737-800 flown by Ukraine International Airlines, which plunged from the sky minutes after takeoff Wednesday morning, killing all 176 people aboard, is fraught with difficulty and intrigue.

Iran has invoked an international agreement to get assistance from other countries — including the U.S. — in investigating Wednesday’s fiery crash of a jetliner near Tehran.

The U.S. National Transportation Safety Board has appointed an investigator to represent the agency but hasn’t sent employees to the scene due to concerns that doing so might violate sanctions. The agency has said it was conferring with the State Department and Treasury on how to proceed.

The prime ministers of Canada, the U.K. and Australia all said on Thursday that they had intelligence showing that the Ukrainian jet was probably brought down by an Iranian missile and called for an international investigation of the disaster. Iran denies those claims.

They didn’t specify the nature of the intelligence, but a person familiar with the inquiry said a U.S. spy satellite detected two missiles being launched from an Iranian battery near where Flight 752 was passing overhead.

--With assistance from Jordan Fabian and Jennifer Jacobs.