WASHINGTON -- U.S. President Barack Obama says there is "no clear evidence" that a gunman who carried out the deadliest mass shooting in U.S. history -- killing 49 people at a gay nightclub in Orlando, Florida -- was "directed" by a broader extremist organization.
Obama said on June 13 that Omar Mateen, a U.S.-born citizen of Afghan descent identified by U.S. authorities as the shooter in the June 12 massacre, was likely influenced by extremists but that no direct evidence suggests he was acting under instructions or was part of a larger plot.
Speaking to reporters at the White House, Obama warned that the investigation was at a "preliminary stage" but said it appears that the 29-year-old Mateen, who proclaimed allegiance to the extremist Islamic State (IS) group during a call to emergency dispatchers made from the nightclub, had been "inspired by various extremist information that was disseminated over the Internet."
"One of the biggest challenges that we are going to have is this kind of propaganda and perversion of Islam that you see generated on the Internet, and the capacity for that to seep into the minds of troubled individuals or weak individuals and seeing them motivated then to take actions against people here in the United States and elsewhere in the world that are tragic," Obama said.
He added that the country must also consider the risks of "lax" laws allowing easy access to "very powerful firearms."
Mateen was shot dead by police who stormed the Pulse nightclub three hours after the killings began there, bringing the total number of dead to 50.
Following the attack, IS called Mateen one of its "soldiers." The IS-linked news agency Amaq, meanwhile, said the attack had been "carried out by an Islamic State fighter."
Despite the statements, however, IS has not officially claimed responsibility for the attack.
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Police said the attacker opened fire with an AR-15 assault rifle and a handgun in the nightclub shortly before 2 a.m., and then held a group of club patrons hostage for three hours before he was killed in a shoot-out.
Fifty-three people were wounded, and many remain in critical condition with multiple gunshot wounds.
Later on June 13, White House spokesman Josh Earnest criticized the Republican-controlled Congress for "inaction" on passing gun-control legislation that would make it more difficult "for any individual to get their hands on a weapon of war."
Earnest specifically cited the AR-15 used by Mateen, which he said is designed for use on the battlefield, not on the streets of Florida.
Obama said investigators are examining the gunman’s potential motives, including whether he deliberately targeted the nightclub because it was a gay venue.
He was speaking in the Oval Office after being briefed on the investigation by top law enforcement officials, including FBI Director James Comey and Homeland Security Secretary Jeh Johnson.
Comey said authorities are "highly confident" that Mateen was "radicalized" at least partially through information he obtained on the Internet. It remains unclear whether he belonged to an established extremist group or what organization he may have been inspired by, he added.
"We'll leave no stones unturned and we'll work all day and all night to understand the path to that terrible night," Comey said.
He added that the FBI is trying to establish whether Mateen had recently scouted Walt Disney World, which is located in Orlando, and other venues as possible attack targets but said he was not in a position to provide further details.
The U.S. entertainment magazine People, citing an unidentified federal law enforcement source, reported on its website earlier on June 13 that Mateen had recently scouted the world-famous amusement park on a visit with his wife.
Authorities said they are investigating whether Mateen may have had assistance in carrying out the killings but emphasized that they believe he was the only attacker in the massacre and that there is no evidence that the public is currently in danger.
"There is an investigation of other persons. We are working as diligently as we can on that," Lee Bentley, the U.S. attorney for the middle district of Florida, told a June 13 news conference. "If anyone else was involved in this crime, they will be prosecuted.
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The presumptive presidential candidates of the two main U.S. political parties weighed in on the mass killing in television interviews.
The Democratic Party’s Hillary Clinton called for more stringent gun-safety measures and increased security efforts, while warning against demonizing Muslims.
"What I don't do, because I think it's dangerous, is to demonize an entire religion, and that plays into Islamic State's hands," Clinton told CNN on June 13.
Addressing a campaign rally in Cleveland, Ohio, later in the day, Clinton said that while the Orlando killer may be dead, "the virus that poisoned his mind remains very much alive, and we must attack it with clear eyes, steady hands, unwavering determination, and pride in our country and our values."
Her Republican rival, wealthy businessman and reality TV star Donald Trump, reiterated his support for a temporary ban on Muslims entering the United States and criticized U.S. Muslims for not alerting authorities of suspicions about Mateen.
He told supporters at a June 13 campaign rally in New Hampshire that he would "suspend immigration" from countries with a "proven history" of terrorism against the United States or other allies "until we fully understand how to end these threats."
"We cannot continue to allow thousands upon thousands of people to pour into our country, many of whom have the same thought process as this savage killer," Trump told the crowd.
Meanwhile, U.S. Secretary of State John Kerry warned against attempts to "point fingers at one group or one form of sectarianism or another, or one religion or another" over the killings.
"Those are not the values of our country," Kerry said on June 13. "What we need to do is bring people together and work to forever prevent this kind of hate and terror from playing out as it has so horribly in the last day."
Statements of sympathy and condemnation have been pouring in from around the world.
In a statement, Afghan President Ashraf Ghani condemned the attack, saying that "targeting civilians is not justifiable under any circumstances whatsoever," while Chief Executive Abdullah Abdullah told the country's cabinet that the incident "tells us that terrorism knows no religion, boundary, and geography. Terrorism must be eliminated."
Paris city hall said the Eiffel Tower will shine in the colors of the rainbow on the night of June 13 to honor the victims of the Orlando tragedy. U.S. and rainbow flags will fly. The rainbow flag is the symbol of the LGBT community. In November, 130 were killed when IS extremists carried out attacks on a music hall, restaurants, and bars in the French capital.
Queen Elizabeth II and Prime Minister David Cameron have sent messages of condolence from Britain, while German Chancellor Angela Merkel has said it's important to continue with "our open, tolerant life" following the Orlando attack.
China's President Xi Jinping has telephoned Obama to express his condolences over the shootings.
Iran, where homosexuality is illegal and can be punishable by death, also condemned the massacre, calling it an "evil... terrorist attack."
"The Islamic Republic of Iran, based on its principled policy of condemning terrorism and its strong will to seriously confront this evil phenomenon, condemns the recent terrorist attack in Orlando," Foreign Ministry spokesman Hossein Jaberi Ansari was quoted by state news agency IRNA as saying on June 13.
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Mateen, the son of Afghan immigrants to the United States, was born in New York and moved to Florida at a young age with his parents.
He had been an armed guard at a gated retirement community and worked for the global security firm G4S for nine years. G4S said he had cleared two company background screenings, the latest in 2013.
G4S said in a statement that it was "cooperating fully with all law enforcement authorities, including the FBI, as they conduct their investigation."
G4S has 623,000 employees worldwide and describes itself as "the largest security solutions provider in the world" on the company website.
Florida state records show that Mateen held a firearms license since at least 2011. Authorities also say Mateen legally purchased at least two firearms within the past week or so.
Mateen married a woman in March 2009 named Sitora Alisherzoda Yusufiy who was born in Uzbekistan and immigrated to the United States. They became separated after just a few months and were legally divorced in 2011.
Yusufiy told the media she had met Mateen online and moved to Florida where she lived with him from April to August 2009. She said he beat her regularly.
"He was mentally unstable and mentally ill," Yusufiy told reporters in Boulder, Colorado.
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The suspect's father, Seddique Mateen, said early on June 12 that he believed his son was motivated by hatred of homosexuals -- not by his Muslim religion.
Seddique Mateen said his son got angry when he saw two men kissing in public in Miami several months earlier in front of his 3-year-old son.
"This had nothing to do with religion," Mateen's father told the media. "I don't know what caused it," Seddique Mateen said. "I never figured out that he had a grudge in his heart...I am grief-stricken."
"We are saying we are apologizing for the whole incident," Seddique Mateen said. "We are in shock like the whole country."
The FBI said its agents twice investigated Mateen for alleged Islamist links but closed those cases after interviewing him.
Special Agent Ronald Hopper said Mateen was first investigated in 2013 after he made inflammatory comments to co-workers alleging possible ties to terrorists.
In 2014, the agency looked into potential ties between Mateen and Moner Mohammad Abusalha, a resident of Fort Pierce, Florida, who carried out a suicide truck-bomb attack in Syria and had appeared in a video released by the Al-Qaeda-linked Al-Nusra Front.
Hopper said the FBI determined that contact between Mateen and Abusalha "was minimal and did not constitute a substantive relationship or a threat at that time."
With reporting by RFE/RL's Radio Mashaal, AP, Washington Post, NBC, Reuters, AP, AFP, BBC, and the Orlando Sentinel.