The shooter who killed at least 50 people and left 53 others injured in a LGBT nightclub in Florida called emergency services and swore allegiance to ISIS, according to police.

Omar Mateen, who shot down at least 50 people at the Pulse nightclub, had security and firearm licenses sine he had been working for G4S security company.

Islamic State has allegedly claimed responsibility for the shooting, according to ISIS-affiliated news agency Amaq. However, an official claim from ISIS has been disputed.

A law enforcement official told NBC News there is no indication that Omar Mateen was in touch with terrorists overseas and nothing to indicate this was a directed attack.

Also, several officials say, there’s no sign that anyone else was involved in the attack, either in helping Mateen or egging him on.

Speaking at the White House, US President Barack Obama called the attack “an act of terror and an act of hate,” and said the FBI would spare no effort to determine whether the suspect had been inspired by any extremist group.

The massacre began when the gunman stormed the Pulse Nightclub about 2 a.m. ET with an AR-15 type rifle and a handgun and started shooting, officials said.

The gunman called 911 before the attack and said he was faithful to ISIS. He twice had been investigated by federally authorities for alleged comments he made about terrorism, but both investigations were closed.