Nato head Jens Stoltenberg has put pressure on Iran to cooperate in a “transparent and thorough investigation” into the Ukrainian passenger plane that crashed near Tehran.
"I call on Iran to fully participate and contribute to a transparent and thorough investigation," Mr Stoltenberg told reporters at an emergency meeting of EU foreign ministers, called in response to escalating tensions between the US and Iran.
"We have no reason to not believe the reports we have seen from different Nato allies ... that the plane may have been downed by Iranian air defence systems," he said.
Ahead of the meeting of the foreign ministers in Brussels, an EU official said Iran needed to allow an “independent and credible” probe into the crash, which killed 176 passengers, most of them Iranian and Iranian Canadian dual nationals.
“It is very important for us that the investigation that takes place happens through an independent and credible civil safety investigation conducted in line with the International Civil Aviation Organisation rules,” European Commission spokesman Stefan de Keersmaecker said.
While he US, UK and Canada have all said it is "highly likely" that Iran shot down the Boeing 737 that crashed during its ascent, other European nations have been less forthright in saying Iran was responsible for the downing of the flight.
Ukraine's President Volodymyr Zelenskiy said "the missile theory is not ruled out, but it has not been confirmed yet."
In a Facebook post, he reiterated his call "on all international partners" - the US, Britain and Canada in particular - to share data and evidence relevant to the crash.
Those nations may hesitate to share information on such a strike because it comes from highly classified sources.
Iran has vehemently denied responsibility for the crash, calling reports, citing US intelligence and defence officials, of a mistaken anti-aircraft missile strike against the passenger jet “psychological warfare”.
Experts from France’s BEA air accident agency and Canadian and US representatives have been asked to join the Iran-led investigations into the Ukrainian International Airlines Flight 752 crash.
Iranian state media reported on Friday that representatives from the three Western nations would be brought into meetings concerning investigations into the crash “as soon as they arrive” in Iran.
They will join investigators from Ukraine who have already arrived in the country to inspect debris from the Flight 752.
French Foreign Minister Jean-Yves Le Drian said earlier France was ready to contribute to the probe.
Iran has also now invited manufacturer Boeing to take part. It had initially said it would not allow the manufacturer to take part in the probe, going against prevailing international norms on crash investigations.
