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 he had “suspicions” about what happened to the plane.
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.
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. It said this information was based on US intelligence, which sources said picked up signals of a radar being turned on.
US satellites also reportedly detected two missile launches shortly before the Ukrainian plane exploded.
Meanwhile, Newsweek quoted US and Iraqi officials as saying they believed the aircraft was hit by a Russia-built Tor M-1 surface-to-air missile system.
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.
The Pentagon has so far made no public comment on the issue.
Meanwhile, when asked what he thought had happened to the plane, President Trump answered: “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.
Earlier on Thursday, Oleksiy Danylov, the secretary of Ukraine’s security and defence council, said in a Facebook post (in Ukrainian) that three four main possible crash causes were being considered:
an anti-aircraft missile strike, specifically a Tor missile, taking into account reports of a missile being found near the crash site
a mid-air collision with a drone or other flying object
engine destruction/explosion due to technical reasons
an explosion inside the plane as a result of a terror attack
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 defence 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.
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.