WASHINGTON (Reuters/AFP) - The father of Omar Mateen, the man identified as the killer in the fatal Orlando gay club shooting, has told the media that the attack "has nothing to do with religion" after the authorities said his son has leanings towards militants of the Islamic State in Iraq and Syria (ISIS).

He described an incident in downtown Miami in which his son saw two men kissing in front of his wife and child and he became very angry.

"We are saying we are apologising for the whole incident," NBC News quoted him as saying. "We weren't aware of any action he is taking. We are in shock like the whole country."

Omar, born in 1986, was a US citizen of Afghan descent and had lived in Port St Lucie, Florida. His father, Seddique Mateen, lives in Florida, according to public records, but it was not immediately known when he came to the United States. He did not immediately return messages left on his phone, which appeared to be turned off, or respond to an email.

Omar Khatab, the owner of the California-based satellite channel Payam-e-Afghan, said in an interview that Seddique Mateen occasionally bought time on his channel to broadcast a show called "Durand Jirga," which focused in part on the disputed Durand Line, the frontier between Afghanistan and Pakistan demarcated by the Indian subcontinent's former British rulers.

"Three or four times a year, he would show up in Southern California," Khatab said in a phone interview on Sunday. "He'd talk for about two to three hours. He'd buy his own time and come here and broadcast and leave within a day."

Khatab said Seddique Mateen's political views were largely anti-Pakistan.

One of Seddique Mateen's videos refers to the "killer ISI" - the acronym for Pakistan's main military-run intelligence service - and says the agency is the "creator and father of the world's terrorism."

US officials have accused Pakistani intelligence of backing violence against US targets in Afghanistan, although Pakistan denies the allegations.

A US congressman said Omar Mateen, a 29-year-old Florida resident and US citizen, may have pledged allegiance to the Islamic State of Iraq and Syria. US officials cautioned that they had no immediate evidence of any direct connection with Islamic State or other foreign extremist group, nor had they uncovered any contacts between the gunman and any such group.

Fifty-three people were wounded in the rampage. It was the deadliest single US mass shooting incident, eclipsing the 2007 massacre of 32 people at Virginia Tech university.

Seddique Mateen interviewed Afghan President Ashraf Ghani in January 2014, according to a video posted on his YouTube channel. The interview touched on economic development and youth unemployment in Afghanistan. Khatab said Mateen conducted the interview in Kabul and brought it to California for broadcast.

But relatives interviewed by US media say Mateen, who worked as a security officer, was not overly religious but had anti-gay views and had regularly assaulted his ex-wife.

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 ex-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 later 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.

He owned a small caliber handgun and worked as a guard at a secure facility for juvenile delinquents.

According to a report by the Daily Beast website, citing FBI sources, Mateen was investigated twice for possible extremist links in 2013 and 2014 but never prosecuted.

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