The father of the suspected gunman who killed at least 50 people at an Orlando, Florida, gay nightclub on Sunday, said the attack "has nothing to do with religion," NBC News reported.

Mir Seddique told the broadcaster that his son, Omar Mateen, who was killed in an exchange of gunfire with police, had become angered after seeing two men kissing in Miami several months ago.

"We are saying we are apologizing for the whole incident. We weren't aware of any action he is taking. We are in shock like the whole country," he is quoted by the network as saying.

Fifty-three others were wounded and the heavy death toll made it the deadliest single shooting incident in U.S. history.

When asked if the FBI suspected that the gunman may have an extremist leanings, including a possible sympathy with Islamic State, Ronald Hopper, an assistant FBI agent in charge, said: "We do have suggestions that the individual may have leanings toward that particular ideology. But right now we can't say definitively."

Police says the shooter was armed with an assault-type rifle, a handgun and some type of suspicious device.