Iran says its armed forces mistakenly launched two surface-to-air missiles at a Ukrainian passenger jet that crashed with 176 people onboard earlier this month, its first acknowledgement of the precise number of rounds fired at the airliner.

Assessments by western intelligence agencies and video footage from the launch site had pointed to two missiles being fired at the Boeing 737-800 on the morning of 8 January, but Iranian officials had so far referenced only one until the release of preliminary report on Tuesday by the country’s civil aviation authority.

The black boxes recovered from the aircraft were still to be examined and could remain so for the time being, the report said. Iranian flight-crash investigators lacked the technology to download data from the aircraft’s black boxes and had asked the US National Transportation Safety Board and its French counterpart for assistance, but neither had “so far responded positively”, it said.

“If devices are provided, the information [on the boxes] can be restored and retrieved in a short period of time,” the report said.

Ukraine has made repeated requests for Iran to send the black boxes to Kyiv for analysis, which an Iranian aviation official was quoted agreeing to do on Saturday, before contradicting himself in remarks carried by state-run media outlets two days later. Canada, which lost 57 citizens onboard the flight, has called for France to handle the investigation.

The report said Russian-made Tor-M1 missiles were launched at the Kyiv-bound Ukraine International Airlines jet shortly after it took off from Tehran at 6.12am local time. The aircraft last contact with air-traffic control at 8,100ft and disappeared from Iranian surveillance radars at 6.18am.

After being struck, it descended over a residential area and crashed in a public park, tearing apart as it moved through a football pitch, farmlands and gardens and killing everyone onboard, investigators said.

The report did not definitively blame the missiles for the crash, saying their impact “on the accident and the analysis of this action is under investigation”.

Footage from the site where the missiles were fired that was published on social media last week showed a 23-second gap between the two launches.

Giancarlo Fiorella (@gianfiorella) This CCTV footage allegedly shows *two* missile launched at #PS752. Prior to the surfacing of this footage there were reports that people in the area heard two explosions/launches.



Working to geolocate now. I'll post some likely spots in a sec. https://t.co/8G1xzmG2ZZ

The aerospace chief of the Iranian Revolutionary Guard Corps, an elite, hardline branch of the Iranian military, said earlier this month a missile operator misidentified the plane as a cruise missile and had a 10-second window to decide whether to fire at the target. “Under such circumstances, he decides to make that bad decision: he engages, the missile is fired, and the plane is hit,” Ali Hajizadeh said.

Iranian air defences around the capital had been bolstered the previous night in anticipation of Iran’s ballistic missile attack on US forces stationed in neighbouring Iraq about five hours before the plane crashed on the same morning.

Those missiles were fired in reprisal for the US’s assassination five days earlier of the Iranian general Qassem Suleimani, the head of the Revolutionary Guards’ external operations and one of the country’s most popular political figures.

Iran had initially blamed the plane crash on a technical malfunction, but doubts over that explanation grew when Ukrainian officials said they were actively investigating the possibility the plane had been shot down. Photos purporting to be from the crash site also showed what appeared to be debris from a Tor-M1 missile.

Officials admitted to accidentally shooting down the plane four days later, triggering protests in Tehran and other cities across the country and a wave of resignations and criticism from journalists at state-run outlets.