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

A military statement on state TV early on Saturday blamed “human error” for the downing of Ukraine International Airlines flight 752 on Wednesday in the tense aftermath of strikes on US targets. It was followed by an apology from Iran’s president and condolences from the supreme leader, Ayatollah Ali Khamenei.

Ukraine’s president, Volodymyr Zelenskiy, responded on Saturday morning that Iran must make an official apology and agree to a full investigation and compensation, as well as cooperating with Ukraine’s own investigators. “Our 45 professionals should have full access and cooperation to establish justice,” a statement from the presidency said.

The Canadian prime minister, Justin Trudeau ,also said his country’s focus remained on “closure, accountability, transparency and justice” for the families of the 57 Canadian victims.

Hassan Rouhani, the Iranian president, 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 Guards, according to the military statement, carried on the official IRNA news agency.

“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 an 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.