Iran has admitted that its military made an “unforgivable mistake” in unintentionally shooting down a Ukrainian jetliner, killing all 176 people onboard, after days of rejecting western intelligence reports that pointed to Tehran being responsible.

A military statement came on Saturday morning via state TV, with “human error” blamed for the downing of Ukraine International Airlines flight 752 on Wednesday. It was followed by an apology from Iran’s president.

President Hassan Rouhani, wrote on Saturday: “The Islamic Republic of Iran deeply regrets this disastrous mistake. “My thoughts and prayers go to all the mourning families. I offer my sincerest condolences.”

The Iranian foreign minister, Javad Zarif, wrote: “A sad day. Preliminary conclusions of internal investigation by armed forces: human error at time of crisis caused by US adventurism led to disaster. Our profound regrets, apologies and condolences to our people, to the families of all victims, and to other affected nations.”

The plane was mistaken for a hostile target after it turned towards a sensitive military centre of the Revolutionary Guard, the military statement carried on the offical IRNA news agency said.

“The military was at its highest level of readiness” amid the heightened tensions with the US, it said, adding: “In such a condition, because of human error and in a unintentional way, the flight was hit.”

The military apologised for the disaster and said it would upgrade its systems to prevent such mistakes in the future. The responsible parties would be referred to a judicial department within the military and held accountable, it said.