ORLANDO (AFP) - Reports on the gunman who attacked a Florida gay nightclub and triggered a shooting that left 50 dead paint a picture of a violent and prejudiced young man.

The suspect, 29-year-old Omar Mateen, is a Muslim-American of Afghan descent and police are investigating whether he may have had a terrorist motive.

US law enforcement is investigating whether he had ties to or was inspired by Islamist extremism, after a source linked to the Islamic State in Iraq and Syria (ISIS) claimed the attack.

And the FBI confirmed that they had received reports that he made a call just before the massacre to claim allegiance to ISIS.

But relatives interviewed by US media say Mateen, who worked as a security officer, was not especially religious.

But he did have anti-gay views and had regularly assaulted a former wife.

Mateen's shocked father Mir Seddique said his son had recently been offended to see two gay men expressing affection on a Miami street.

"We were in downtown Miami, Bayside, people were playing music," the father told NBC News in the immediate aftermath of the shooting.

"And he saw two men kissing each other in front of his wife and kid and he got very angry," Mr Seddique said.

The father is a minor celebrity in Afghan political circles, hosting an occasional television show in which he expressed hardline views.

In the "Durand Jirga Show", available on YouTube, he rails against the Pakistani government and announces a quixotic bid to seek the Afghan presidency.

Sunday's attack, which became the worst mass shooting in modern US history, was carried out in the Pulse nightclub, a well-known gay hangout.

"We are in shock like the whole country," Mr Seddique added. "This had nothing to do with religion."

In a separate interview, a former wife of the suspect who left him in 2011 fearing for her life, said he was violently abusive.

"He was not a stable person," the former wife told the Washington Post, which did not identify her because she fears for her safety.

"He beat me. He would just come home and start beating me up because the laundry wasn't finished or something like that," she told the Post.

According to the wife's account the pair had met in New York but in March 2009 had moved in together in Fort Pierce, Florida.

The woman's parents rescued her from the relationship and the pair were later divorced, according to a court document seen by AFP.

She described him as a "private person" but not especially expressive about his Muslim faith.

In a separate interview with the Washington Post, the leader of the Fort Pierce mosque where Mateen prayed described him as a quiet man.

"He would come and pray and leave. There was no indication at all he would do something violent," Imam Shafiq Rahman told the paper.

Imam Rahman said Mateen would attend prayers with his father and three-year-old son.

The imam's son, however, described Mateen as "an aggressive person" who used to work out regularly.

Mateen owned a small caliber handgun and worked as a guard at a secure facility for juvenile delinquents. Police said he bought an assault rifle before the attack.

According to the FBI, Mateen was investigated twice for possible extremist views and contact with a US suicide bomber in 2013 and 2014 but never prosecuted.

According to the Florida Department of Agriculture and Consumer Services website, he had a gun license set to expire in September of next year.