Islamic State has claimed responsibility for the Orlando nightclub shooting, which killed 50 people and injured 53 others, according to the Amaq news agency, which is tied to the group.
“The armed attack that targeted a gay nightclub in the city of Orlando in the American state of Florida which left over 100 people dead or injured was carried out by an Islamic State fighter,” Amaq said.
The Islamic State claim comes after US media reported that a man, suspected to have been the gunman, swore allegiance to IS in a 911 call around the time of the attack.
He also reportedly mentioned the 2013 Boston Marathon bombings, according to CNN.
A number of officials have cautioned, however, that possible links between the gunman and Islamic State have not been confirmed.
Florida Senator Bill Nelson said the IS claim, which does not specify whether the terrorist group was directly involved in the attack, has not been verified.
The gunman, who is among the dead, has been named as 29-year-old Omar Mateen of Port St. Lucie Florida, a US citizen of Afghan descent.
Armed with a device thought to be a bomb, an assault rifle and a handgun, Mateen opened fire in the busy club Pulse in the early hours of Sunday morning before taking hostages.
He was involved in a three-hour stand-off with officers before SWAT teams stormed the building and shot him dead.
US President Barack Obama has condemned the massacre as an “act of terror and an act of hate”.
Confirming earlier that the number of dead had risen from 20 to 50, Orlando Mayor Buddy Dyer told a press briefing: “Today we’re dealing with something that we never imagined and is unimaginable.
“There’s blood everywhere”.
He said a state of emergency has been declared in the city of Orlando and that he had asked Florida’s governor to issue a state-wide state of emergency due to the “scale of the crime”.