Iran's military has confirmed that it "unintentionally" shot down a Ukrainian passenger jet - with the country's president describing it as an "unforgivable mistake".
A statement from the Iranian military blames "human error" for the downing of the plane.
All 176 people on board the plane were killed.
The statement explains that the downing happened in the hours after Iranian authorities launched a number of missile strikes against bases in Iraq, in retaliation for the US assassination of top general Qasem Soleimani.
Tehran's military officials claim they were on high alert for American planes in the wake of the strikes.
Their statement says: "In such a sensitive and critical situation, flight 752 of Ukraine Airlines which had taken off from Imam Khomeini International Airport, moved very close to a sensitive military spot belonging to the IRGC forces when completing a loop.
"The altitude and the direction of the flight's movement were like an enemy target, so the aircraft was targeted unintentionally due to human error."
The Iranian military says it apologises for the 'human error', and expressed its condolences to the families of victims.
Iranian President Hassan Rouhani has pledged an investigation will work towards prosecuting the perpetrators of "this unforgivable mistake".
The US, Canada and UK had previously confirmed they'd seen intelligence indicating the plane had been downed by an Iranian missile.
However, the overnight statement marks the first Iranian acknowledgement of their involvement in the crash.
Reacting to Tehran's admission, Ukraine's president said it was not a good morning - but added that it finally brought the truth.
Volodymyr Zelensky said in a statement: "We insist on full admission of guilt.
"We expect assurances of readiness for a full and open investigation from Iran, bringing those responsible to justice, repatriation of bodies of the dead, payment of compensation, official apologies through diplomatic channels."
He added that he hopes the investigation into the crash "will continue without artificial delays and obstacles", and that his country's investigators "need full access and engagement to establish justice".
All 176 people on board the plane were killed in the crash - including 82 Iranians, 11 Ukrainians, 10 people from Sweden, four passengers from Afghanistan, three from Germany and four British nationals.
Some 63 Canadians were also among those who died - with Prime Minister Justin Trudeau describing it as a "tragedy that not only shocked Canada, but the rest of the world".