Iran on Saturday admitted shooting down a Ukrainian plane early this week killing 176 people on spot in one of the worst tragedies.
This comes a day after Canada insisted that it had intelligence that the plane was brought down by Iranian missiles.
United States President Donald Trump also said that he was suspicious of the plane crash, calling for more investigations.
Iran's statement on Saturday morning blames "human error" for the incident.
Press TV also quoted Iran's General Staff of the Armed Forces as saying that the plane had flown close to a "sensitive military site".
Iranian President Hassan Rouhani wrote that the country "deeply regrets this disastrous mistake."
"My thoughts and prayers go to all the mourning families. I offer my sincerest condolences," he said, adding that "investigations continue to identify and prosecute this great tragedy and unforgivable mistake."
Iranian Foreign Minister Javad Zarif said that "human error at time of crisis caused by US adverturism led to the disaster."
"Our profound regrets, apologies and condolences to our people, to the families of all victims, and to other affected nations."