Iranian president, Hassan Rouhani, has assured that the crime will not go unpunished and that a "thorough investigation" will be carried out in order to establish responsibilities. 

Rouhani said: "It is an unforgivable mistake… one person cannot be held responsible."

He added: "The Iranian armed forces who admit their mistake is a good first step. But we must make sure that it never happens again."

Rouhani also said that his government was "accountable to the Iranians and the other nations who lost lives in this accident. For our people, it is very important in this accident that anyone who has been at fault or neglect on any level be prosecuted. Everyone who should be punished will be punished."

The Ukrainian civilian plane was hit by a missile outside Tehran on January 8. All 176 people on board were killed.