Trump has 'suspicions' over crash amid reports Iran 'downed plane'

"I have my suspicions," Trump said.

"It was flying in a pretty rough neighborhood and somebody could have made a mistake."

The president's remarks came as Newsweek, CBS and CNN reported that the plane had been accidentally shot down by Iranian air defence systems, citing unnamed US and Iraqi intelligence officials.

All 176 people on board died in the crash, which occurred shortly after the Ukraine International Airlines flight took off from Tehran's Imam Khomeini International Airport.

"Some people say it was mechanical. I personally don't think that's even a question," Trump said, adding that "something very terrible happened".

The crash took place on Wednesday morning, just hours after Iran launched a volley of more than 20 missiles at two military bases in Iraq.

The barrage of missiles came in retaliation against US forces hosted in the two bases after a US drone strike killed top Iranian commander Qasem Soleimani last week.

Suspicions over the cause of the crash immediately turned to a possible downing of the plane by a surface-to-air missile due to the short time between the two incidents.

US officials are "confident" Iran shot down the Boeing 737 jet, sources told CBS on Thursday.

According to the sources, US intelligence observed signals of a radar being turned on shortly before the crash. US satellites also detected two surface-to-air missile launches before the plane exploded.

Federal officials briefed on the intelligence earlier on Thursday were told missile components were found near the crash sites, CBS reported.

Both CNN and Newsweek also reported that US officials believe Iran mistakenly shot down the jet.

"It could be very possible, CNN is told, that this is a fog of war incident," Pentagon correspondent Barbara Starr said.

"The Iranian missile unit, the troops on the ground in Iran at that point, perhaps saw something on their own radar returned, perhaps thought they were under attack and fired."

Iran's civil aviation authority on Wednesday formed an investigation into the crash, which said earlier on Thursday that airliner had not called for help but had turned back en route to the Tehran airport after experiencing a problem shortly after take-off.

Tehran has said it will not turn over the plane's two black boxes to US investigators or the plane's manufacturer, Boeing.

Ukrainian President Volodymyr Zelensky, said a team of 45 crash investigators from his country had arrived in Iran to assist in the probe, saying he expects them to be present at the black box inquiry.

"Undoubtedly, the priority for Ukraine is to identify the causes of the plane crash," he said on Thursday. "We will surely find out the truth."

Kiev has said it is considering a full range of causes for the crash, including engine failure, drone collission, a bomb and a missile strike.

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