ORLANDO, United States – US anti-terror strategy came under fresh scrutiny after a gunman previously cleared of jihadist ties launched a hate-fueled rampage in a Florida gay club that left 50 people dead.
The Islamic State of Iraq and Syria (ISIS) group has claimed it was behind Sunday's carnage at the Pulse nightclub, the worst mass shooting in modern US history.
It said in a radio bulletin Monday, June 13, that the attack on the "crusader gathering" was carried out by "one of the soldiers of the caliphate."
World leaders joined in condemning the murderous assault, which triggered grief and shock but also defiance in the gay and lesbian community as monuments from New York to Paris were being lit up in memory of the victims.
Terrified survivors described how the gunman raked clubgoers with bullets, prompting a police SWAT team to storm the venue and shoot dead the attacker, identified as 29-year-old Omar Mateen.
The FBI admitted that Mateen had previously been investigated – but cleared – for ties to a US suicide bomber.
Special Agent Ronald Hopper also said Mateen was reported to have made a 911 call pledging allegiance to IS shortly before the massacre.
"We know enough to say that this was an act of terror and an act of hate," US President Barack Obama said.
The Orlando assault is being treated as the worst act of terror on US soil since the September 11, 2001 attacks claimed by Al-Qaeda.
Monday's claim on Al-Bayan radio followed a report by the IS-linked news agency Amaq on Sunday that the attack had been "carried out by an Islamic fighter."
Red flags
Mateen was born to Afghan parents in New York in 1986 and lived in Port St Lucie, Florida, about a two-hour drive from Orlando.
His father Mir Seddique told NBC News his son may have been motivated by homophobia, insisting: "This had nothing to do with religion."
The suspect's ex-wife, who divorced him in 2011, told reporters he had been violently abusive to her but was not especially religious.
But Hopper told reporters Mateen's behavior had raised red flags well before Sunday's attack.
In 2013 he was probed by the bureau after making inflammatory comments to co-workers that suggested terrorist ties.
In 2014 he was again questioned by agents investigating his contacts with Moner Mohammad Abusalha, a fellow Floridian.
Abusalha became notorious as the first US citizen to carry out a suicide bombing in Syria, and was reportedly a member of an Al-Qaeda affiliate.
"We determined the contact was minimal and did not constitute a substantive relationship or a threat at that time," Hopper said.
The Orlando atrocity came at the height of what is already a heated US presidential election campaign.
Democratic flag-bearer Hillary Clinton postponed a campaign rally with Obama and tweeted that her "thoughts are with those affected by this horrific act."
Her Republican rival Donald Trump lost no time in claiming the attack proved he was right to promise a ban on Muslims entering the US.
Trump demanded Obama resign for failing to publicly blame the massacre on "radical Islam," and vowed to make a speech on security policy Monday.
"If we do not get tough and smart real fast, we are not going to have a country anymore," Trump declared.
Paul Ryan, speaker of the House of Representatives, echoed Trump's line: "As we heal, we need to be clear-eyed about who did this. We are a nation at war with Islamist terrorists."
'I'm trapped'
Events at Pulse unfolded over a three-hour period from around 2:00 am (0600 GMT) Sunday, when shots rang out amid the throbbing music.
Witness Janiel Gonzalez described scenes of mayhem as the gunman sprayed revelers with bullets.
"It was like complete chaos," he told Agence France-Presse. "It was like a scene out of a movie. People were screaming 'Help me, help me, I'm trapped!'"
"People were getting trampled. There was no clear exit sign at the club, so we didn't know which door to take or where to go."
Police said the gunman was armed with an assault rifle and a handgun.
A policeman working "extra duties" at the club responded and, along with two other officers, exchanged fire with the suspect.
Police stormed the venue after the suspect fell back inside, and broke through a wall with a wheeled armored vehicle known as a BearCat.
It was unclear whether all the victims were killed by the gunman or if some died in crossfire during the assault to rescue hostages.
Relatives break down
Relatives of victims gathered at a hotel near Orlando Regional Medical Center to hear authorities read out the names of those hospitalized.
People broke down when names of loved ones names were not read out, suggesting they had died.
A relieved Angel Colon found his son, 26-year-old Angel Jr, alive and in stable condition with three gunshot wounds.
"When I saw him, I held him," Colon said. "I told him in Spanish: 'Pai, God is giving you another chance'."
The massacre – which coincided with Gay Pride month in the United States -- cast a long shadow over a parade in Los Angeles parade where more than 100,000 marched.
Chillingly, a man was arrested in nearby Santa Monica with weapons and explosives in his car.
Police said he had no known connection to the Orlando bloodshed.
In New York, the Tony Awards for musical theatre went ahead as planned but were dedicated to the victims of the massacre.
The Empire State building went dark, while the spire of One World Trade Center was lit in the rainbow colors of the gay pride flag.
In Paris, the Eiffel Tower was also to be illuminated Monday night in rainbow colors. – Federica Narancio with Dave Clark in Washington, Agence France-Presse / Rappler.com