The US government believes Iran accidentally shot down a Ukraine airliner that crashed in Iran, killing all 176 people aboard, three US officials told Reuters on Thursday.

Citing an extensive review of satellite data, one official said the US government had concluded with a high degree of certainty that Iranian anti-aircraft missiles brought down the plane.

The officials said the plane had been tracked by Iranian radar before the missiles were fired.

The data showed 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, one of the officials said.

That was quickly followed by an explosion in the vicinity of the plane, this 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."