The Islamic State in Iraq and Syria (ISIS) on Sunday claimed responsibility for a deadly shooting in an Orlando gay nightclub.

“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,” ISIS said in a statement.

Fifty people died and 53 others were injured in what is being described as the worst mass shooting on American soil.

(Related: 50 killed in Orlando gay nightclub; worst mass shooting in U.S. History.)

A lone gunman, Omar Mateen, 29, died in a shootout with police.

Several outlets reported that Mateen pledged allegiance to ISIS in a 911 phone call.

The FBI has not confirmed a connection to ISIS.