France said on Friday it was ready to join the investigation into the crash of a Ukrainian airliner in Iran that killed all 176 people abroad, after Canada and others said the plane had been brought down by an Iranian missile, probably by mistake.
Ukraine said it could not rule out a missile strike but that had not been confirmed. Iran denied a missile brought down the Boeing 737-800 shortly after take off.
French agency BEA helped analyse data from the flight recorder of a crashed Boeing plane in Ethiopia last year. Iran's state television showed footage purportedly of two black boxes, the voice and flight data recorders, from the Ukrainian plane.
The Ukraine International Airlines flight to Kiev from Tehran crashed on Wednesday, as Iran was on alert for a U.S. military response hours after firing missiles at U.S. targets in Iraq.
The incident adds to international pressure on Iran, after months of tension with the United States and then tit-for-tat military strikes. Washington killed an Iranian general last week in a drone attack in Iraq, prompting Tehran's missile launches.
In social media posts, ordinary Iranians voiced anger at their authorities for not closing the airport after Iran's missile launches. Scores of those on board were Iranians with dual nationality.
Canadian Prime Minister Justin Trudeau, citing intelligence from Canada and other sources, blamed an Iranian missile for bringing down the plane that had 63 Canadians on board, although he said it "may well have been unintentional."
"The evidence indicates that the plane was shot down by an Iranian surface-to-air missile," he said.
France said it was ready to join Canada and other nations contributing to the investigation. "It is important that as much clarity as possible is made and as quickly as possible," French Foreign Minister Jean-Yves Le Drian said.
An Iranian official had earlier said France might be involved as it was one of the countries where the plane's engines are made.
Ukrainian President Volodymyr Zelenskiy said a missile strike could not be ruled out but it had not been confirmed.
A U.S. official, citing satellite data, said Washington had concluded with a high degree of certainty that anti-aircraft missiles brought down the plane in error.
A U.S. official said data showed the plane airborne for two minutes after departing Tehran when heat signatures of two surface-to-air missiles were detected. There was an explosion in the vicinity and heat data showed the plane on fire as it fell. U.S. military satellites detect infrared emissions from heat.
The New York Times said it had obtained a video appearing to show an Iranian missile hitting a plane near Tehran airport.
U.S. President Donald Trump told reporters he did not believe the crash of the airliner was due to a mechanical issue, saying "somebody could have made a mistake - on the other side."
A defence expert said the plane's radar signature would have been similar to a large U.S. military transport plane.
Iran denied the Ukrainian airliner had been hit by a missile, saying such reports were "psychological warfare against Iran."
"All those countries whose citizens were aboard the plane can send representatives and we urge Boeing to send its representative to join the process of investigating the black box," government spokesman Ali Rabiei said in a statement.
Iran's civil aviation organisation said in an initial report less than 24 hours after the incident that the three-year-old airliner, which had its last scheduled maintenance on Monday, encountered a technical problem after takeoff and was heading to a nearby airport before it crashed.
Investigations into airliner crashes require cooperation of regulators, experts and companies across jurisdictions. They can take months and initial reports in 24 hours are rare.
Iran said bodies and body parts recovered from the site of the crash were taken to the coroner's office for identification.
Ukraine has outlined four potential scenarios, including a missile strike and terrorism. Kiev said its investigators wanted to search the crash site for possible debris of a Russian-made missile used by Iran's military.
The Transportation Safety Board of Canada said it was making arrangements to tour the site after an Iranian invitation.
The U.S. National Transportation Safety Board (NTSB) said it had designated an accredited representative to join the probe and was determining the level of participation.
Boeing said it would support the NTSB. The company is still reeling from two deadly crashes of 737 MAX planes, including the one in Ethiopia, that led to the plane's grounding in March 2019.
The 737-800 that crashed was built in 2016 and is the prior generation of the 737 before the MAX.