Kyiv, Ukraine - The US media reports that Iran might have mistakenly shot down the UIA Boeing 737 that crashed on Jan. 8 shortly after it took off from Tehran with 176 people on board.
US officials say they believe the Ukrainian International Airlines Boeing 737-800 was shot down by a missile.
Ukraine earlier said it was examining whether a missile strike brought down the aircraft - but Iran ruled this out. The crash came just hours after Iran carried out missile strikes on two airbases housing US forces in Iraq.
CBS News quoted US intelligence sources as saying a satellite detected infrared "blips" of two missile launches, followed by another blip of an explosion.
Meanwhile, Newsweek quoted a Pentagon and senior US intelligence officials, as well as an Iraqi intelligence official, as saying they believed the Ukrainian plane was hit by a Russian-made Tor missile.
US President Donald Trump said on Thursday that "I have my suspicions" over the plane. "Somebody could have made a mistake," he said.
Amid tensions heightened by the US killing of top Iranian general Qasem Soleimani on 3 January, Iran has said it will not hand over the recovered black box flight recorders to Boeing, the plane's manufacturer, or to the US.
Under global aviation rules, Iran has the right to lead the investigation, but manufacturers are typically involved.
What does the US media report?
In separate reports, CBS News and Newsweek said US and Iraqi intelligence officials were confident the Ukrainian plane was brought down by a missile fired by Iran.
CBS published a brief report on Twitter, saying the officials were confident the plane was shot down.
It said this information was based on US intelligence, which sources said picked up signals of radar is turned on. US satellites also reportedly detected two missile launches shortly before the Ukrainian plane exploded.
Meanwhile, Newsweek quoted the US and Iraqi officials as saying they believed the aircraft was hit by a Russia-built Tor M-1 surface-to-air missile system, known as Gauntlet by Nato.
Two Pentagon officials assessed that the incident was accidental, Newsweek added. It quoted sources as saying that Iran's anti-aircraft systems were probably active following its attacks on the US airbases.
Meanwhile, asked at what he thought happened to the plane, President Trump said: "I have my suspicions. It's a tragic thing when I see that, it's a tragic thing. But somebody could have made a mistake on the other side.
Some people say it was mechanical. I personally, I don't think that's even a question, personally. So we'll see what happens. Something very terrible happened. Very devastating,
Mr. Trump said.
Mr. Danylov said Ukrainian investigators, who are already in Iran, wanted to search for possible debris from a missile at the site of the crash. Iran is known to have Russian missile defense systems.
The investigation would include experts who worked on the investigation into the 2014 downing of Malaysia Airlines flight MH17 in eastern Ukraine, Mr Danylov added.
The UK government said it was urgently looking into reports that the Ukrainian plane may have been shot down.
Prime Minister Boris Johnson's spokesman said reports in media were "very concerning" and the government wanted to see a "full, transparent investigation".
What does Iran say?
Iran's Civil Aviation Organisation (CAOI) chief Ali Abedzadeh said: "The plane, which was initially headed west to leave the airport zone, turned right following a problem and was headed back to the airport at the moment of the crash."
Mr. Abedzadeh added that witnesses saw the plane "on fire" before the crash and that pilots had not made any distress calls before trying to return to Imam Khomeini airport.
"Several domestic and foreign flights were flying in Iranian space at the same altitude of 8,000ft (2,400m). The issue of the missile's impact on the aircraft cannot be true in any way," he said.
Mr. Abedzadeh said the initial findings had been sent to Ukraine and the US, where Boeing has its headquarters.
He was earlier quoted as saying that "terrorism" had played no role in the crash.
Sweden and Canada had also been sent the findings, as their nationals were on board, he added.
Who is investigating the crash?
Normally, the US National Transportation Safety Board would have a role to play in any international investigations involving US-made Boeings. But the board must act with permission and in accordance with the legislation of the foreign country concerned.
We will not give the black box to the manufacturer and the Americans. This accident will be investigated by Iran's aviation organisation, but the Ukrainians can also be present,
Mr. Abedzadeh, said
Mr. Abedzadeh also added that it was not yet clear which country would analyze the black boxes - a cockpit voice recorder and flight data recorder.
Ukrainian President Volodymyr Zelensky earlier said that "a thorough and independent investigation will be conducted in accordance with international law", and that he would speak to Iranian leaders to step up co-operation in investigating the crash.
Ukraine is observing a day of national mourning on Thursday.
Boeing said it was "ready to assist in any way needed", while Canadian Prime Minister Justin Trudeau said his country expected to have a role in the investigation and had offered technical assistance.
What do we know?
The Ukraine International Airlines flight PS752 to Kyiv had 167 passengers and nine Ukrainian crew on board.
The majority of passengers were from Iran and Canada.
Ukraine's Tehran embassy initially blamed engine failure but later removed the statement, saying any comment regarding the cause of the accident prior to a commission's inquiry was not official.
There was good visibility when the plane went down near Iran's capital, according to the Flightradar24 aviation website. Officials from the airline said the crew was experienced.