US intelligence officials believe that the Ukraine International Airlines plane that crashed in Iran on Wednesday with 176 people on board was downed by an Iranian missile, multiple US media reports said on Thursday. 

CBS News reported that intelligence officials have evidence to back up the belief. The report said that US intelligence picked up signals of a radar being turned on, detected two surface-to-air missile launches just before the plane exploded.

Boeing 737 jet of Ukraine International Airlines crashed shortly after taking off from Tehran's Imam Khomeini airport on Wednesday, killing all 176 people aboard.

The plane crash came shortly after the Iranian forces launched more than a dozen missiles targeting US bases in Iraq. 

Officials, however, believe that the plane was not an intended target and was a mistake. 

US President Donald Trump conveyed similar "suspicions" on Thursday, saying that "somebody could have made a mistake." 

Iran had on Wednesday said it will not hand over the black box of the crashed Ukrainian airline jet to US planemaker Boeing. 

The head of Tehran's civil aviation organisation said while the agency has decided not to send the black box to the US company, it is not clear which country it would be sent to so that its data could be analysed.

While the first statement by Ukraine's embassy in Iran referred to engine failure, its second statement said the causes had not been disclosed and that any previous comments were not official.

The plane was carrying 167 passengers and nine crew members from different countries including 82 Iranian nationals. There were also 11 Ukrainians and 63 Canadians on board the flight.