Several people have been detained in Iran over the accidental shooting down of a Ukrainian passenger plane with a missile.
Iran also detained 30 people involved in protests that have swept the nation for four days since the military belatedly admitted its error.
President Hassan Rouhani said the probe would be overseen by a special court.
A Ukrainian International Airlines flight was brought down shortly it took off from Tehran last Wednesday, killing all 176 people on board.
Most of the victims were Iranian and Canadian citizens.
For the first three days after the crash, Iran denied that its armed forces had shot down the airline and suggested there had been a technical failure.