Tehran said on Thursday US media reports that Iran had had accidentally shot down a Ukrainian aircraft--killing all 176 people on board two days ago--made 'no sense'. 

A Ukraine airliner crashed outside Tehran after taking off, a few hours after Iran fired missiles at two military bases in Iraq that housed US troops, escalating tensions with Washington. 

US media reported that unnamed American officials had claimed Iran had shot down the plane mistakenly. President Trump hinted towards the possibility, saying "something terrible had happened". 

"I have my suspicions," he said. "It was flying in a pretty rough neighborhood and somebody could have made a mistake. Some people say it was mechanical. I personally don´t think that´s even a question."

Analysts pointed to pictures shared widely online of the wrecked fuselage of the aircraft showing multiple apparent puncture holes consistent with a rocket that detonated just outside the plane, blasting shrapnel into it.

"Similar marks were visible on wreckage of MH17," CNN reporter Jim Sciutto said, referring to the Malaysian Airlines flight which was shot down only July 17, 2014 over Eastern Ukraine by a Russian-designed surface-to-air missile.

Iran, on the other hand, denied the reports, saying that many international airliners were at the time flying over the country. 

"Several internal and international flights were flying at the same time in Iranian airspace at the same altitude of 8,000 feet (2,440 metres)," said Iran's transport ministry. 

Ali Abedzadeh, head of Iran´s civil aviation organisation and deputy transport minister, responded to rumours on social media networks that the Revolutionary Guards' had fired missiles at the aircraft by mistake. 

He said Iran was in the process of retrieving information from the black box of the aircraft to ascertain the cause of the crash. 

"But if more specialised work is required to extract and analyse the data, we can do it in France or another country," he said. 

Iranian authorities said there were indications the plane had turned back after facing problems. A team of Ukrainian experts flew in and joined the investigation on the ground Thursday.