Sitora Yusufiy told reporters suspect was not especially expressive about his Muslim faith
The man suspected of shooting dead at least 50 people at a gay nightclub in Florida has been described by his ex-wife as a violent person who was "mentally ill".
Omar Mateen, 29, was a Muslim American born in New York of Afghan descent and police are investigating whether the shooting was a hate crime or whether he had links to the terror group.
His former wife Sitora Yusufiy told how her parents had to rescue her from the violent marriage after just four months.
She said the pair had met in New York before marrying and moving to Florida together in 2009 in what, at first, seemed like a normal marriage.
But he began to beat her and, with the help of her parents, she left him, fearing for her life. The couple divorced in 2011.
The woman, Sitora Yusufiy, said: "He was not a stable person.
"He beat me. He would just come home and start beating me up because the laundry wasn't finished or something like that."
She said the pair had met in New York but had moved to Florida together in March 2009 and that he had expressed interest in being a police officer, even going as far as applying to the police academy.
She described him as a "private person" but said he was not especially expressive about his Muslim faith.
Mateen owned a small calibre handgun, which was licensed, and worked as an armed guard at a secure facility for young offenders. He had been employed by security company G4S since September 2007.
He earned an associate's degree in criminal justice technology from Indian River State College in 2006, said college spokesman Michelle Abaldo, quoted in the New York Times.
IS-linked news agency Amaq said a statement: "The attack that targeted a nightclub for homosexuals in Orlando, Florida and that left more than 100 dead and wounded was carried out by an Islamic State fighter."
Mateen died in what the FBI described as "an exchange of gunfire with police officers".
FBI Assistant Special Agent Ron Hopper said Mateen was investigated in 2013 after making "inflammatory comments to co-workers alleging possible terrorist ties".
Mr Hopper said that matter was "thoroughly investigated" and Mateen was interviewed twice but "ultimately we were unable to verify the substance of his comments and the investigation was closed".
In 2014, he was investigated again for his possible relationship with US suicide bomber Moner Mohammad Abu-Salha but Mr Hopper said: "We determined contact was minimal and did not constitute a substantive relationship or a threat at the time".
US media reported that Mateen made a phone call before the Orlando attack to declare his allegiance to the IS leader Abu Bakr al Baghdadi.
Responding to these reports, Mr Hopper said: "There were 911 calls in which there was conversation between the subject and law enforcement representatives and 911 dispatchers. That has become federal evidence.
"It's my understanding - I have not personally listened to them - but it was general to the Islamic State."
He added that Mateen was "not under investigation at the time of the incident and was not under surveillance".
A spokesman for the Bureau of Alcohol, Tobacco, Firearms and Explosives said Mateen had bought a handgun and a long gun "within the last week or so" and was legally able to do so.
Meanwhile, his father Seddique Mir Mateen, a life insurance salesman, told NBC News that the killings had "nothing to do with religion" but were motivated by homophobia.
He said his son recently lashed out in his presence after witnessing a gay couple embracing in downtown Miami.
"He saw two men kissing each other in front of his wife and kid and he got very angry," Mr Seddique said.
He added: "We are saying we are apologising for the whole incident.
"We are in shock like the whole country," he said.
Mateen attended evening prayer services at his local Islamic Centre three or four times a week, most recently with his young son, according to Iman Syed Shafeeq Rahman, who said that he was not very social, although he showed no signs of a violent nature.
"When he finished prayer he would just leave," Mr Rahman told The Associated Press. "He would not socialise with anybody. He would be quiet. He would be very peaceful."
Mr Rahman said he thought the attack was more due to psychological issues Mateen may have had, rather than any anti-American sentiment.
He added: "My personal opinion is that this has nothing to do with ISIS."