ORLANDO, the United States, June 13 (Xinhua) -- The lone gunman who killed 49 and wounded 53 at a popular gay nightclub in Orlando, Florida, did pledge allegiance to the Islamic State (IS) and tried to negotiate with police during the attack, said Orlando Police Chief John Mina at a morning news briefing on Monday.

"He was cool and calm when he was making those phone calls to us," Mina said. "We had a team of crisis negotiators that did talk to the suspect just trying to get as much information as possible ... He really wasn't asking for a whole lot. We were doing most of the asking."

At the briefing, an FBI agent clarified that the total number of nightclub victims was 49 instead of the previously reported 50, a number that counted the shooter himself as a victim.

"The shooter is not a victim," FBI Special Agent in Charge Paul Wysopal told reporters.

The shooter, identified as Omar Mateen, a 29-year-old who was of Afghan descent but born in the United States, parked his car before 2 a.m. on Sunday outside the Pulse nightclub, walked into the crowded main room with an assault rifle and a handgun, and opened fire minutes later on the crowds. He then took several hostages and holed himself up.

More than three hours later, Mateen emerged through a hole that a police armored vehicle had made in the building to rescue hostages, and was killed during the gun battle with SWAT forces, Mina said at the briefing.

"The suspect came out of that hole himself ... and engaged in a gun battle with officers, where he was ultimately killed," he said.

"Rumors of multiple shooters are unfounded. The one shooter, Omar Mateen, is dead," the police chief added.

A third weapon as well as some terrorism-related documents have been found in the shooter's car by the FBI, according to local media reports.

The ongoing investigation in the deadliest mass shooting in U.S. history is still in the early stage, the reports quoted U.S. Attorney Lee Bentley as saying.

Florida Governor Rick Scott has asked President Barack Obama to sign a disaster declaration for the state following the shooting, the reports added.