Iran on Saturday admitted to unintentionally shooting down a Ukrainian plane with over 170 passengers on January 8. President Hassan Rouhani expressed deep regret and called it a “disastrous” and “unforgivable” mistake.

Iran had earlier denied reports linking it to the air crash, and had even called the claims “psychological warfare”.

Rouhani tweeted: “Armed Forces’ internal investigation has concluded that regrettably missiles fired due to human error caused the horrific crash of the Ukrainian plane [and] death of 176 innocent people. Investigations continue to identify [and] prosecute this great tragedy [and] unforgivable mistake...My thoughts and prayers go to all the mourning families. I offer my sincerest condolences.”

The Ukrainian International Airlines aircraft crashed on the outskirts of Tehran soon after Iran had bombed two airbases in Iraq used by United States military forces.

Iran’s admission came after leaders of at least three countries said that evidence suggested Tehran had a role to play in the disaster. There were 82 Iranians and 63 Canadians on the plane, with nine of the 176 people on board being crew members.

A statement on Tehran’s state television the responsible parties would be held accountable, The Guardian reported. “The military was at its highest level of readiness,” it said. “In such a condition, because of human error and in a unintentional way, the flight was hit.”

Iran’s Foreign Minister Javad Zarif tweeted on Saturday to say that the air crash was due to “human error”, but he also blamed it on the “crisis caused by US adventurism”. “Our profound regrets, apologies and condolences to our people, to the families of all victims, and to other affected nations,” he added.

Ties between the US and Iran have plummeted after the western nation killed Iran’s top military commander Qassem Soleimani on January 3.

The United States on Friday slapped new sanctions on Iran to cut off “billions of dollars” of support to the country as tensions continued.

Pressure on Iran

On Friday, Canadian Prime Minister Justin Trudeau, United Kingdom’s Boris Johnson and Australia’s Scott Morrison claimed they had received information of Iran’s involvement in the plane crash. “We have intelligence from multiple sources including our allies and our own intelligence,” said Trudeau. “The evidence indicates that the plane was shot down by an Iranian surface-to-air missile.”

Johnson said he had received inputs about the flight being shot down by a missile attack from Iran, The Telegraph reported. However, he added: “This may well have been unintentional.”

Australian Prime Minister Morrison on Friday made a similar comment about the intelligence, but added there was “nothing to suggest now at this point an intentional act”, The Sydney Morning Herald reported. He also called for an investigation into the matter “that would include undertaking all efforts to ensure we get recovery of the black box recorder that can obviously inform that investigation.”