Spokesman Gholamhossein Esmaili said investigations into the incident were continuing, but provided no details.
President Hassan Rouhani said the probe would be overseen by a "special court".
Ukrainian International Airlines flight PS752 was brought down shortly it took off from Tehran on 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 Boeing 737-800 and suggested there had been a technical failure.