Ukraine's President Volodymyr Zelenskyy has said he and his Iranian counterpart Hassan Rouhani have agreed in a phone call to identify the remains of those deceased on Ukraine Airlines Flight 752 in the near future and to begin joint work on decoding the black boxes of the crashed plane.

Zelenskyy on Saturday said Ukrainian experts were continuing their work in Tehran and that their findings meant the truth about the crash could not be concealed.

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He also urged Ukraine's international partners to remain united and persistent until the investigation was complete.

Zelenskyy thanked the international community - Canada, the United States and the United Kingdom in particular - for their support in the wake of the plane crash just outside Tehran on Wednesday.

Earlier on Saturday, Iran said its military had shot down the Ukrainian plane killing all 176 on board in a "disastrous mistake", adding that air defences were fired in error while on alert after Iranian missile strikes on US targets in Iraq.

In a televised address, Zelenskyy promised that his government would compensate the families of the victims.

Shortly afterwards, Ukrainian Prime Minister Oleksiy Honcharuk said Ukraine would pay 200,000 hryvnia ($8,350) each to the families of those who died in the plane crash.

He said Ukraine International Airlines would make payments to the families of the crew members who died in the crash. The airline's spokeswoman was not immediately available for comment.

'Erroneous actions'

Iranian President Rouhani on Saturday called Zelenskyy to officially apologise to Ukraine for accidentally shooting down the passenger plane.

"[Rouhani] apologised on behalf of the Iranian side for the tragedy that took 176 lives," a statement from Zelenskyy's office read.

"The President of the Islamic Republic of Iran fully acknowledges that the tragedy was caused by the erroneous actions of the military of this state."

During the call, Rouhani assured Zelenskyy that those involved in the incident would be held accountable.

"It is extremely important for us to return the bodies of the deceased to Ukraine next week - by January 19 - so that their relatives can bid a final farewell," Zelenskyy said, according to the statement.

Iran's Supreme Leader Ayatollah Ali Khamenei offered his condolences and ordered the armed forces to address "shortcomings" so that such a disaster does not happen again.

The acknowledgement came after officials in Iran had for days categorically denied Western claims that the Ukraine International Airlines plane was struck by a missile.