This story has been updated.
The suspect in the overnight mass shooting at a gay nightclub in Orlando, Florida that left at least 50 dead and 53 injured has been identified, according to multiple reports.
Omar Saddiqui Mateen, 29, of Fort Pierce, Florida, who was shot and killed by police, was reportedly a U.S. citizen born in the state of New York and his family is from Afghanistan, according to The Washington Post.
Mateen, who worked as a private security guard, made the two-hour trip to Orlando in a rented vehicle, according to CNN.
(ALSO: Authorities in California said they arrested a man who sources said was headed to Sunday's Los Angeles Pride Parade with explosive powder, assault weapons and a camouflage outfit.)
NBC News reports that Mateen pledged his support to the terrorist group ISIS and its leader Abu Bakr al-Baghdadi in a 911 call during the shooting.
Authorities are investigating the early Sunday morning shooting spree at Pulse as an act of terrorism, CNN reports.
The death toll makes it the worst mass shooting in United States history. The number of casualties had initially been estimated to be 20 early Sunday morning.
With many of the injured in critical condition, the death toll is expected to rise.
Mateen reportedly entered the club at about 2 a.m. with an assault-type rifle, handgun and possibly other hand-held devices, and then took hostages for about three hours until police storm the club, according to The Washington Post. The attack appears to have been "organized and well-prepared," according to CNN.
Pulse has described itself as Orlando's "hottest gay bar."
The incident occurred barely 3½ miles from the theater where a killer shot "The Voice" singer Christina Grimmie before turning the gun on himself.
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