MOSCOW (AP) - The father of a Chechen immigrant killed in Florida while being interrogated by the FBI about his ties to a Boston Marathon bombings suspect said on Thursday that the US agents killed his son "execution-style".

At news conference in Moscow, Abdul-Baki Todashev showed journalists 16 photographs that he said were of his son, Ibragim Todashev, in a Florida morgue. He said his son had six gunshot wounds to his torso and one to the back of his head and the pictures were taken by his son's friend, Khusen Taramov.

It was not immediately possible to authenticate the photographs.

The FBI said 27-year-old mixed martial arts fighter Ibragim Todashev was killed last week during a violent confrontation in his Orlando home while an FBI agent and two Massachusetts state troopers questioned him about his ties to slain Boston Marathon bombing suspect Tamerlan Tsarnaev, as well as about a 2011 triple slaying in Massachusetts.

Three law enforcement officials said initially that Mr Todashev had lunged at the FBI agent with a knife, although two of them later said it was no longer clear what had happened.

Greg Comcowich, a spokesman for the Boston FBI, declined to comment on Thursday on the elder Todashev's claim that his son was unarmed.

Abdul-Baki Todashev said the photos were emailed to him by Mr Taramov, who apparently was at the morgue to identify the body. The father said Mr Taramov was part of the Muslim community holding the body for the family until they could retrieve it.

The father said Mr Taramov told him that US agents interrogated him on the street while five officials interrogated Mr Todashev in his Florida house for eight hours on May 22, the night he was shot.

He said his son was "100 per cent unarmed".

He added that his son moved to the US in 2008 on a study exchange programme and met Mr Tsarnaev at a boxing gym in Boston in 2011, about a year before he moved to Orlando. He said the two were "not particularly close friends".

Prior to last month's bombings, Mr Todashev underwent an operation for a sports injury and was on crutches, making it physically impossible for him to have been involved in the bombings, his father said. He added that his son had recently received a green card and was planning to return to Chechnya for the summer last Friday, two days after he was killed.

The father said he and his brother were interviewed at the US Embassy in Moscow on Thursday as they sought a visa to take his son's body back to Chechnya.

FBI agents interrogated the younger Todashev twice before the night he was shot, his father said.