The father of a Chechen immigrant to the US, who died while being interrogated by the FBI about ties to a Boston Marathon bombings suspect, has said that agents killed his son "execution style".

At a news conference on Thursday in Moscow, Abdulbaki Todashev showed journalists 16 photographs he said were of his son, Ibragim, in a Florida morgue.

Todashev  said his son, who was shot last week, had six gunshot wounds to his torso and one to the back of his head, and said the pictures were taken by his son's friend, Khusen Taramov.

"My son didn't have any weapons," he said. "They questioned him for eight hours - eight hours! That's an entire working day. You question a person for eight hours and you can provoke him to do anything.

"But my son didn't have a gun, didn't have a knife. Supposedly there's information that he went to the kitchen and took a knife and threw himself on it - they discussed that version of events at one stage," said Todashev.

It was not immediately possible to authenticate the photographs he presented of his son.

"I've only ever seen or heard of these kinds of things in movies: that they would shoot my son, I mean shoot a person, and then just in case shoot him in the head," said Todashev.

"I want justice and I want there to be an investigation. I want them to try these people according to American law.

"These aren't employees of the FBI, they're just bandits, that's all that I can call them."

The FBI says 27-year-old Ibragim Todashev was killed during a violent confrontation on May 22 while being questioned about ties to killed Boston Marathon bombing suspect Tamerlan Tsarnaev, as well as about a 2011 triple killing in Massachusetts.

US media on Wednesday quoted unamed law enforcement as stating that Todashev had lunged at an FBI agent and overturned the table, but had neither a gun nor a knife.

Source: Agencies