DAMASCUS - The Islamic State (IS) group hailed the gunman behind the attack on a gay nightclub in Florida as a "soldier of caliphate," according to a bulletin over the group's Al-Bayan radio on Monday.

The suspect was identified by US authorities as 29-year-old Omar Mateen, an American citizen of Afghan descent, who had reportedly called 911 and claimed allegiance to the IS before going on a spree of shooting at the Pulse nightclub in Orlando, Florida, killing and wounding over 100 people.

A day earlier, the IS-linked news agency Amaq said that the Islamist militant group was responsible for the shooting.

"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," said Amaq in a short English statement posted online Sunday evening.

At least 50 people were killed and 53 others wounded, including a police officer, in the shooting, the deadliest terror attack in the US since the 9/11 terror attacks in 2001.