The victims of the worst mass shooting in American history.

Terrorist Omar Mateen shot dead 50 people and wounded at least 53 more during the massacre at the Pulse nightclub in Orlando in the early hours of Sunday morning – and called 911 just before the attack to pledge allegiance to ISIS.

Mateen, 29, of Port St. Lucie in Florida, reportedly laughed as he sprayed bullets into the crowded club before he was shot dead by a SWAT team several hours after launching his horrific massacre with a legally bought assault rifle and pistol.

Although US officials do not know if the attack was directed by ISIS, Mateen, who worked as a security guard, was inspired by the terror group and has been investigated by the FBI twice over his suspected terror links. He also attended the same Mosque as an American suicide bomber.

ISIS's Amaq news agency said the terror group was responsible for the shooting and says Mateen was one of its fighters. During the attack, Mateen also referenced the 2013 Boston Marathon bombing, a Massachusetts State Police spokesman said on Sunday.

Donald Trump called for President Barack Obama to resign after he did not blame radical Islam for the attack in his remarks following the shooting, referring to it instead as an 'act of terror' and an 'act of hate.'

Trump also congratulated himself, saying that he 'called it' when he touted a ban on all Muslim immigrants entering the United States in the wake of the terrorist attack in San Bernardino,

California, in December last year - despite the fact that Mateen was an American citizen.

Mateen, who has a wife and young son, has been described as a 'mentally ill' loner who beat his ex-wife for not completing household chores and became enraged when he saw two men kissing months before launching his attack.

So far, 21 victims have been officially identified by the city of Orlando on its website.

On Sunday, Edward Sotomayor Jr., 34; Stanley Almodovar III, 23; Luis Omar Ocasio-Capo, 20; Juan Ramon Guerrero, 22; Eric Ivan Ortiz-Rivera, 36; Peter O. Gonzalez-Cruz, 22; Luis S. Vielma, 22 and Kimberly Morris, 37, were confirmed dead.

In the early hours of Monday morning, Eddie Jamoldroy Justice, 30; Darryl Roman Burt II, 29, Deonka Deidra Drayton, 32; Alejandro Barrios Martinez, 21; Anthony Luis Laureanodisla, 25; Jean Carlos Mendez Perez, 35; and Franky Jimmy Dejesus Velazquez, 50, were added to the list.

Later on Monday the authorities announced the names of a further six of the 50 who died: Amanda Alvear, 25, Martin Benitez Torres, 33, Luis

 Daniel Wilson-Leon, 37, Mercedez Marisol Flores, 26, Xavier Emmanuel Serrano Rosado, 35, and Gilberto Ramon Silva Menendez, 25, were all killed at Pulse.

Shortly after making the 911 call, Mateen entered the crowded nightclub at around 2am carrying an AR-15 and started spraying the helpless crowd with bullets.

Witnesses said he fired relentlessly - 20 rounds, 40, then 50 and more. In such tight quarters, the bullets could hardly miss. He shot at police. He took hostages. Around 5am, authorities sent in a SWAT team to rescue them, Police Chief John Mina said.

The shooter exchanged gunfire with 14 police officers at the club, which had more than 300 people inside.

'He had an automatic rifle, so nobody stood a chance,' said Jackie Smith, who had two friends next to her get shot. 'I just tried to get out of there.'

When the gunfire finally stopped, 50 were dead and dozens critically wounded. Thirty-nine of the dead were killed at the club, and 11 people died at hospitals, the mayor said.