Omar Mateen, the gunman responsible for the Orlando gay nightclub shooting, has pledged allegiance to the ISIS.
The attack killed at least 50 people and left several others wounded.
Mateen, identified as a U.S.-based Afghan national, pledged his allegiance to the terror group during a 911 call.
He called the dispatchers around 20 minutes post the attack and mentioned the Boston Marathon bombers, CNN quoted a U.S. official as saying.
The attacker, who died in a shootout with the police, had reportedly been questioned earlier by the FBI in connection with two different terror related incidents. No conclusive evidence was, however, found against Mateen, who was on the agency's radar for being a suspected ISIS sympathizer.
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U.S. President Barack Obama condemned the attack calling it "an act of terror and an act of hate", the New York post reported.
Mateen, who worked as a security officer at G4S Secure Solutions, legally purchased the assault weapons within the last few days.
Sitora Yusufiy, the gunman's ex-wife, has said that he was abusive, emotionally unstable and suffered from mental illness.
