Orlando gunman Omar Mateen pledged allegiance to Islamic State

The gun attack on a gay nightclub in Orlando, Florida which killed at least 50 people in the early hours of Sunday has been described by the US president as the deadliest mass shooting in American history.

The gunman in what is the worst terror attack on US soil since the al-Qaeda attacks of September 11th, 2001 was named as Omar Seddique Mateen (29), a US citizen born in New York to Afghan parents who lived in Fort Pierce, about 120 miles southeast of Orlando.

US president Barack Obama called the attack at Pulse nightclub "an act of terror and an act of hate".

"Today marks the most deadly shooting in American history," he said during a brief statement from the White House in which he again raised concerns about the ease of access to weapons in the United States.

The Orlando suspect called 911 before the attack and pledged allegiance to Islamic State, according to FBI agent Ronald Hopper. He also referenced the brothers who carried out the 2013 Boston Marathon bombing.

Mr Hopper told reporters in Orlando that Mateen was interviewed twice by the bureau – in 2013 about inflammatory comments he made to work colleagues claiming potential ties to terrorists, and in 2014 about his possible connections with Moner Mohammad Abusalha, the first American to carry out a suicide attack in Syria.

The FBI closed the investigation in 2013, when they were unable to verify the comments he made and the following year found his contact with Abusalha was minimal. Despite those interviews, Mateen was legally able to buy two firearms in the past week, an ATF federal investigator said.

Mateen’s family suggested the attack by the married father-of-one may have been a hate crime aimed at the lesbian, gay, bisexual and transgender community. The suspect’s father, Mir Seddique told NBC News that his son, who was a security guard, became enraged when he saw two men kissing in front of his wife and son (3) on a recent trip to Bayside, in Miami.

Father apologises

“We are apologising for the whole incident,” said Mr Seddique.

“We weren’t aware of any action he is taking. We are in shock like the whole country. This had nothing to do with religion.”

Republican candidate Donald Trump caused outrage over a self-congratulatory tweet about his tough stand on Islamic extremism.

“Appreciate the congrats for being right on radical Islamic terrorism,” he tweeted. “I don’t want congrats, I want toughness and vigilance. We must be smart!”

The attack on the nightclub, filled with about 300 people, during LGBT Pride month, began at 2.02am (7.02am in Ireland) when a police officer working at the club exchanged fire with a gunman who then went inside and took hostages. About three hours later, a special weapons and tactics (Swat) police team raided the club and exchanged gunfire with the suspect, who was with hostages, killing him.

Inside, police found scores dead and injured.

Assault rifle

Orlando police chief

John Mina

said the gunman used an assault rifle – an AR-17 semi-automatic with large capacity rounds of bullets that has become a signature of US mass shootings – and a handgun.

The suspect’s ex-wife told the Washington Post that he was mentally unstable and violent during a two-year marriage that ended in 2011.

Relatives of those caught up in the attack have recalled the dramatic moments when their loved ones found themselves cornered by the suspected gunman.

Mina Justice said her son Eddie texted when the attack began and asked her to contact the police. He told her he ran into a bathroom to hide with others and texted: “He’s coming.”

“The next text said: ‘He has us and he’s in here with with us,’ ” she said.

“That was the last conversation.”

The Irish Embassy in Washington DC is monitoring developments but has not had any requests for consular assistance.