Iran acknowledged on Tuesday that its forces had fired two surface-to-air missiles at a Ukrainian passenger plane that crashed this month near Tehran, confirming for the first time that more than one missile was launched at the jet.

The Iranian authorities also asked officials in the US and France to send the equipment needed to decode the jet’s flight data recorders, or “black boxes,” a request certain to frustrate countries that have called for greater international involvement in investigating the disaster, which killed all 176 onboard.

The downing of Ukraine International Airlines Flight 752 on January 8 came amid heightened tensions between Iran and the US that included tit-for-tat military strikes, and after the killing of the top Iranian security commander, Major General Qassem Soleimani, in a US drone strike at the Baghdad airport.

The plane was shot down the same day Iran fired missiles at two military bases in Iraq that house US troops, in retaliation for the killing of General Soleimani.

After days of denials, Iranian officials acknowledged that the downing was the result of “human error”, prompting angry protests across Iran.

A preliminary report from Iran’s Civil Aviation Organisation, released on Tuesday, corroborated a video verified by The New York Times last week that showed two missiles, fired from a military site, exploding near the plane.

Iranian investigators had established that two Tor-M1 missiles had been fired at the plane, the statement said, adding that the investigation was looking into their effect on the crash.

The crash’s victims included 82 Iranians, 57 Canadians and 11 Ukrainians, heightening calls for an international investigation.