TEHRAN: Iran said that the misalignment of an air defence unit's radar system was the key "human error" that led to the accidental downing of a Ukrainian passenger plane in January.

"A failure occurred due to a human error in following the procedure" for aligning the radar, causing a "107-degree error" in the system, the Iranian Civil Aviation Organisation (CAO) said in a report late Saturday.

This error "initiated a hazard chain" that saw further mistakes committed in the minutes before the plane was shot down, said the CAO document, presented as a "factual report" and not as the final report on the accident investigation. Flight 752, a Ukraine International Airlines jetliner, was struck by two missiles and crashed shortly after taking off from Tehran's main airport on January 8, at a time of heightened US-Iranian tensions.

The Islamic republic admitted several days later that its forces accidentally shot down the Kiev-bound plane, killing all 176 people on board.