Ukraine said Friday Iran was ready to hand over the black box flight recorders of the Ukrainian passenger plane downed by an Iranian missile.

The Kiev-bound Ukraine International Airlines Boeing 737, crashed shortly after taking off from Tehran last Wednesday, killing all 176 people on board, mostly Iranian and Canadian citizens.

Ukraine's foreign minister said Iran would grant a team of investigators from Iran and Canada as the countries that have lost the most nationals access to the recorders.

"After that, the Iranian side is ready to separately transfer the black boxes to Ukraine," Vadym Prystaiko told lawmakers during a parliamentary session.

"This is consistent with international standards, although we still demand that they be given to us immediately to ensure the independence and objectivity of the investigation," Prystaiko said.

Most of the victims were Iranian and Canadian citizens
Most of the victims were Iranian and Canadian citizens AFP / Walter Tychnowicz

After initial denials, the Islamic republic admitted it has shot down the plane "unintentionally" while on high alert after firing missiles at US troops stationed in Iraq in retaliation for the killing of top Iranian commander Qasem Soleimani by a US strike.

Prystaiko told CNN on Wednesday that Kiev has "good cooperation" with Tehran on the crash probe, but lacked "access to the information stored in the black boxes."

"We just want to know that nobody will be tampering with the recordings themselves," he said.

Prystaiko said an Iranian official will visit Kiev next week "to apologise officially and provide explanations."

On Thursday, Canada, Ukraine, Sweden, Afghanistan and Britain issued a five-point plan for cooperation with Iran during the investigation, calling for "full and unhindered access" for foreign officials.