Orlando: US authorities on Monday were investigating whether a gunman who killed 49 people at a nightclub in Orlando and declared his allegiance to IS militants had received any help in carrying out the massacre.
The FBI and other agencies were looking at evidence inside and in the closed-off streets around the Pulse nightclub, where New York-born Omar Mateen perpetrated the deadliest mass shooting in US history, and the worst attack on US soil since the September 11, 2001.
Mateen, 29, the son of Afghan immigrants, was shot and killed by police who stormed the club with armoured cars early Sunday morning after a three-hour siege.
Law enforcement officials were looking for clues as to whether anyone had worked with Mateen on the attack, said Lee Bentley, the US attorney for the middle district of Florida.
"There is an investigation of other persons. We are working as diligently as we can on that," Bentley said at a news conference. "If anyone else was involved in this crime, they will be prosecuted."
Officials stressed they believed there had been no other attackers and had no evidence of a threat to the public.
FBI Director James Comey said authorities still were trying to determine Mateen's motives but there was no indication he was part of an organised terror network, although he may have been inspired by them.
"There are strong indications of radicalisation by this killer and of potential inspiration by foreign terrorist organisations," Comey told reporters in Washington.
"We're highly confident this killer was radicalized at least in some part through the internet." Mateen's rampage began about 2 a.m. Sunday (0600 GMT) when the club was packed with some 350 revelers.
Many fled as the gunman raked the crowd with bullets from an AR-15-style semiautomatic rifle and a pistol.
An initial wave of officers charged into the club and trapped Mateen in a bathroom, Orlando Police Chief John Mina told reporters.
That allowed many patrons to flee, although others were trapped in the restroom with Mateen, leading to the standoff.
"We were able to save and rescue dozens and dozens of people," Mina said.
Police negotiated with Mateen for about three hours before breaking a hole in the wall, which allowed hostages to escape.
Mateen also emerged from the hole and was shot dead by officers, police said. Officials said on Sunday the death toll was 50. On Monday they clarified that the figure included Mateen.
Some 53 people were wounded and 29 remain hospitalised at Orlando Regional Medical Center, the hospital said on Twitter.
By Monday morning, all but one of those killed had been identified and about half the families of the dead had been notified, officials said. Other family members were desperate for news about their missing loved ones.
Julissa Leal, 18, and her mother drove to the Florida city from Lafayette, Louisiana, in search of her brother, 27-year-old Frank Hernandez. They knew he was at the club with his boyfriend, who lost him in the chaos.
"We haven't heard anything, don't know anything," Leal said, fighting back tears. "I'm going to see him again. I'm going to see him again."
During phone calls with authorities in the middle of the rampage, Mateen mentioned support for the leader of IS, the Boston Marathon attackers and a Florida man who became an Al Nusra Front suicide bomber in Syria, Comey said.
Al Nusra is an Al Qaeda offshoot at odds with IS.
Mateen's father said his son was not radicalised.
His ex-wife described him as mentally unstable and violent toward her.
IS reiterated on Monday a claim of responsibility but that did not mean it directed the attack because it offered nothing to indicate coordination with the gunman.
President Barack Obama denounced the attack as an act of terror and hate and said on Monday that the gunman seemed to have been inspired by extremist ideas.
"As far as we can tell right now, this is certainly an example of the kind of homegrown extremism that all of us have been so concerned about for a very long time," Obama told reporters at the White House.
The attack reignited the debate over how best to confront violent extremist militancy and immediately became a sharp point of disagreement in the campaign for the November 8 presidential election.
Democratic candidate Hillary Clinton, in her first campaign stop since the shootings, said in Cleveland that the United States should walk a fine line in bolstering security without demonising Muslims. But she also called for tougher gun safety measures and increased efforts to remove Islamic State messages from the internet.
Wealthy businessman and presumptive Republican nominee Donald Trump lashed out at Obama over the shooting massacre, saying it is possible the president "doesn't want to see what's happening."
In a series of television interviews, he questioned Obama's motivation and said he would never solve the national security problem.
In interviews with CNN and Fox News, Trump criticised the US Muslim population for not reporting suspicions to authorities, and reiterated his call for a temporary ban on Muslims entering the country.
The carnage early on Sunday occurred in the heart of Orlando, about 15 miles (25 km) northeast of the Walt Disney World Resort.
The city is one of the most popular tourist destinations in the United States, drawing some 62 million visitors a year.
Mateen was an armed guard at a gated retirement community, and had worked for the global security firm G4S for nine years.
He had cleared two company background screenings, the latest in 2013, according to G4S..
Mateen's father, Seddique Mir Mateen, said in an interview at his home in Port Saint Lucie, Florida, that he was angered by his son's actions. "Even though he is my son I admit this is terrorist act. This is terrorising. I don't forgive him," the father said.
"If you see his wife, what she is going through his poor wife and his son 3-1/12 years old, such a nice son, he should've thought about that." Mateen's former wife, Sitora Yusufiy, told reporters near Boulder, Colorado, that she had been beaten by Mateen during angry outbursts in which he would "express hatred towards everything."
Authorities said on Sunday that Mateen had been twice questioned by FBI agents in 2013 and 2014 after making comments to co-workers about supporting militant groups, but neither interview led to evidence of criminal activity.
Mateen visited Saudi Arabia in 2011 and 2012 for religious pilgrimages, a government spokesman said on Monday.
The attack came six months after a married couple in California - a US-born son of Pakistani immigrants and a Pakistani-born woman he married in Saudi Arabia - killed 14 people at an office holiday party in San Bernardino.
The couple, who were inspired by IS, died in a shootout with police hours after the mass shooting.