Florida, An American-born man who killed at least 50 people at a gay nightclub in Orlando has been identified as Omar Mateen.

According to reports, "Mateen was a U.S. citizen with no apparent criminal history, was born to Afghan parents in New York in 1986 and was living in Port St. Lucie, Fla".

Mateen had committed himself to ISIS before carrying out the bloodiest mass murder in US history at a gay nightclub in Orlando on Sunday, officials said.

According to a U.S. official, Mateen called 911 during the attack to pledge allegiance to ISIS and mentioned the Boston Marathon bombers.

Mateen carried an assault rifle and a pistol into the packed Pulse club about 2 a.m. Sunday and started shooting, killing 50 people and wounding at least 53, police said.

After a standoff of about three hours, while people trapped inside the club desperately called and messaged friends and relatives, police crashed into the building with an armored vehicle and stun grenades and killed Mateen.