Iran's civil aviation chief denied Friday that a missile downed a Ukrainian airliner which crashed killing all 176 on board, rejecting Western claims of a catastrophic mistake by Tehran's air defences.
Ukraine said its experts had been granted access to the black box flight recorders, as US Secretary of State Mike Pompeo repeated it was "likely" an Iranian missile had downed the plane.
Iran's latest denial came as Tehran faced mounting international pressure to allow a "credible" investigation into the crash, which several Western governments have blamed on an accidental missile strike.
"One thing is for certain, this airplane was not hit by a missile," Iran's civil aviation chief Ali Abedzadeh said, after Tehran invited the US, Ukraine, Canada and others to join the investigation.
The Boeing 737 crashed on Wednesday shortly after Iran launched missiles at US forces in Iraq in response to the killing of top Iranian general Qassem Soleimani in a US drone strike in Baghdad.
It is Iran's worst civil aviation disaster since 1988 when the US military said it shot down an Iran Air plane over the Gulf by mistake, killing all 290 people on board.
The majority of the passengers on Ukraine International Airlines (UIA) Flight PS752 were dual national Iranian-Canadians but also included Ukrainians, Afghans, Britons and Swedes.
Vadym Prystaiko, the foreign minister of Ukraine which has sent around 50 experts to Tehran to take part in the Iran-led inquiry, told reporters Friday: "Our team has now access to the black boxes".
The Ukrainian team also had access to the radio exchanges between the UIA pilots and air traffic control and were receiving "full co-operation" from Iran, said Prystaiko.
The team, granted access to plane fragments and the crash site, will start analysing the contents of the black boxes and their conclusions will be made public, he added.
Pompeo, echoing several world leaders including Canadian Prime Minister Justin Trudeau and British Prime Minister Boris, said "we do believe it's likely the plane was shot down by an Iranian missile".
"We are going to let the investigation play out before we make a final determination," he added Friday.
Trudeau said intelligence sources indicated an Iranian surface-to-air missile downed the aircraft after it took off from Tehran.
"We know this may have been unintentional. Canadians have questions, and they deserve answers," he said.
Abedzadeh rejected the claim."Any remarks made before the data is extracted (from the plane's black box flight recorders) is not an expert opinion," he said."
Video footage, verified by The New York Times, emerged that appeared to show the moment the airliner was hit.
It shows a fast-moving object rising at an angle into the sky before a bright flash is seen, which dims and then continues moving forward.
Several seconds later an explosion is heard and the sky lit up.
Iran said a 10-member Canadian delegation was on its way to help with the probe, a rarity since the two countries cut diplomatic relations in 2012.
Tehran also invited US plane maker Boeing to "participate" in the investigation.
Canada and the US National Transportation Safety Board said they received the invitations and would join the probe.
France is the co-manufacturer of the plane's engines, and has offered its expertise decipher the black box data.
Abedzadeh said Tehran had invited "Americans, Canadians, the French, Ukrainians and the Swedish" to be present during the investigation.
European Union foreign ministers, meeting for crisis talks on tensions in the Middle East, urged Iran to be transparent.
"The important thing now is that everything is completely investigated. Nothing must be swept under the table," German Foreign Minister Heiko Maas said.
US President Donald Trump has indicated that Washington officials believed the Kyiv-bound Boeing 737 was struck by an Iranian missile. "I have my suspicions somebody could have made a mistake."