People stand near the wreckage of a Ukraine International Airlines plane that crashed near Imam Khomeini airport in Tehran on Wednesday. All 167 passengers and nine crew were killed when it crashed shortly after taking off on Wednesday, Iranian state media reported. Photo: AFP

 Iran has confirmed two missiles were fired at a Ukrainian airliner brought down this month, in a catastrophic error that killed all 176 people on board and sparked protests.

The country's civil aviation authority said it has yet to receive a positive response after requesting technical assistance from France and the US to decode black boxes from the downed airliner.

The Kiev-bound Ukraine International Airlines plane was accidentally shot down shortly after takeoff from Tehran's Imam Khomeini International Airport on January 8.

Iran has come under mounting international pressure to carry out a full and transparent investigation into the disaster.

"Investigators... discovered that two Tor-M1 missiles... were fired at the aircraft," Iran's Civil Aviation Organization said in a preliminary report posted on its website late Monday.

It said an investigation was ongoing to assess the bearing their impact had on the accident.

The statement confirms a report in The New York Times which included video footage appearing to show two projectiles being fired at the airliner.

The Tor-M1 is a short-range surface-to-air missile developed by the former Soviet Union that is designed to target aircraft or cruise missiles.

Iran had for days denied Western claims based on US intelligence reports that the Boeing 737 had been shot down.

It came clean on January 11, with the Revolutionary Guards' aerospace commander Brigadier General Amirali Hajizadeh accepting full responsibility.

But he said the missile operator who opened fire had been acting independently.

The deadly blunder triggered days of student-led protests mainly in the Iranian capital. Supreme leader Ayatollah Ali Khamenei said on Friday that the demonstrations were unrepresentative of the Iranian people and accused the country's enemies of exploiting the air disaster for propaganda purposes.

In its report, the Civil Aviation Organization said it was "impossible" for it to read the flight data and cockpit voice recorders - commonly known as black boxes - because they were so advanced.

But it suggested Iran wants to keep them for now.

The 737 was downed when Iran's air defenses had been on high alert hours after its armed forces fired more than 20 ballistic missiles at US troops stationed in Iraq.

That was carried out in reprisal for a January 3 US drone strike that killed Iran's most prominent military commander, Qasem Soleimani, near Baghdad airport.

US President Donald Trump had been poised to retaliate for the missile attack, but refrained, saying the missiles caused no ­casualties. But later the US military said 11 were injured.