WASHINGTON (Reuters) – A Ukraine airliner that crashed in Iran, killing all 176 people aboard, was most likely brought down accidentally by Iranian anti-aircraft missiles, U.S. officials said on Thursday.

According to satellite data, one U.S. official said, the Ukrainian International Airlines Boeing 737-800 bound for Kiev was airborne for two minutes after departing Tehran when the heat signatures of two surface-to-air missiles were detected.

That was quickly followed by an explosion in the vicinity of the plane, the official said. Heat signature data then showed the plane on fire as it went down.

Iran’s head of civil aviation was quoted by ISNA News Agency as saying that it was “impossible that a missile hit the Ukrainian plane.”

Two U.S. officials said Washington believed the downing of the plane, which occurred at a time of rising tensions between Iran and the United States, was accidental.

An Iranian report on Thursday cited witnesses on the ground and in a passing aircraft flying at a high altitude as saying the plane was on fire while in the air.

U.S. President Donald Trump said on Thursday the deadly crash could have been a mistake and he did not believe it was a mechanical issue.

Boeing and the Federal Aviation Administration declined to comment on Thursday, as did the Pentagon.

Boeing is still reeling from two deadly crashes of 737 MAX planes in five months that led to the plane’s grounding in March 2019. The 737-800 that crashed was built in 2016 and is the prior generation of the 737 before the MAX. Boeing has built about 5,000 of those planes, which has a good safety record.

(Reporting by Mark Hosenball, David Shepardson, Jonathan Landay and Phil Stewart; Writing by Tim Ahmann; Editing by Ross Colvin and Sonya Hepinstall)