Messages of solidarity with the LGBT community and condemnation of the attack continued to pour in from political and religious leaders from around the world into the early hours of Monday morning.

US President Barack Obama led the reactions, saying that the shooting at Pulse nightclub in Orlando, Florida was the "most deadly shooting in American history."

A long-time campaigner for stricter gun laws, Obama added that the "brutal murder of dozens of innocent people" was yet another reminder of how easy it is to access a deadly weapon in the US.

"We have to decide if that's the kind of country we want to be," he said. "To actively do nothing is a decision as well."

Forty-nine killed and the shooter, 53 injured

Omar Mateen, a US citizen with Afghan roots, opened fire at the gay nightclub early Sunday morning. At least 49 people were killed and 53 others injured. Seven of the victims have so far been named - Stanley Almodovar III, Luis Omar Ocasio-Capo, Juan Ramon Guerrero, Edward Sotomayor Jr, Eric Ivan Ortiz-Rivera, Peter O Gonzalez-Cruz and Luis S Vielma.

The 29-year-old gunman was killed at the scene in an exchange of fire with 11 police officers.

A law enforcement official told the AP news agency that the gunman had made a call to the emergency services from the club, claiming allegiance to the leader of the so-called "Islamic State" (IS), Abu Bakr al-Baghdadi. IS has made a claim of responsibility for the attack via a website.

'This is a hate crime'

In light of the the suspected links to IS, the head of a prominent US Muslim advocacy group strongly condemned the massacre, calling IS members an "aberration."

Nihad Awad, executive director of the Council on American-Islamic Relations, also called for unity and urged politicians not to "exploit" Sunday's tragedy.

"This is a hate crime. Plain and simple," Awad told a news conference, adding that it "violates our principles as Americans and as Muslims."

"Let me be clear, we have no tolerance for extremism of any kind," he said.

German Foreign Minister Frank-Walter Steinmeier also expressed his condolences to the victims of the attack. "I am shocked by the murderous attack in Orlando. We mourn the victims. Our thoughts are with our friends in the USA," Steinmeier said in a tweet.

Pope Francis, head of the Catholic Church, expressed "the deepest feelings of horror and condemnation," while the British monarch, Queen Elizabeth II, said she and Prince Philip "have been shocked by the events."

Hashtags including #LoveisLove and #GaysBreakTheInternet also began trending on Twitter, as social media users shared their grief and solidarity with the LGBT community.

On the red carpet at the Tony Awards in New York City, several stars, including "The Walking Dead" actress Danai Gurira and ceremony presenter James Cordon, were seen sporting a silver ribbon in tribute to the victims.

Vigils were also held in cities across the world, including Miami, Paris and outside the White House in Washington, DC. In New York, crowds gathered at the "Stonewall Inn," which is an important site in the history of the gay rights movement.

Gunman's background

More details also emerged late on Sunday regarding the background of the gunman. Mateen's ex-wife Sitora Yusufiy said he was an emotionally and mentally disturbed man with a violent temper.

The FBI also confirmed that authorities had become aware of Mateen in 2013 after he made inflammatory comments to co-workers, indicating sympathy for Islamist militants.

The FBI special agent in charge, Ron Hopper, said Mateen was investigated and interviewed twice but the intelligence service was "unable to verify the substance of his comments."

'Not a subtantive threat'

At the time, Mateen worked as a security guard at G4S, a British-owned multinational company that is among the world's largest private security firms.

He joined the company in September 2007 and carried a gun as part of his duties as an armed security officer, G4S said.

In 2014, Mateen was investigated and interviewed for a second time over suspicions that he was connected to Moner Mohammad Abu-Salha - an American citizen who became a suicide bomber in Syria in 2014.

Hopper said, however, that Mateen's contact with Abu-Sallah was minimal and it was deemed at the time that "he did not constitute a substantive threat."

LA Gay Pride parade

In a separate incident on Sunday, police in Los Angeles arrested a man who apparently intended to "harm" the Los Angeles Gay Pride parade.

Santa Monica police chief Jacqueline Seabrooks said that a 20-year-old male was caught with multiple assault rifles, high-capacity magazines ammunition as well as some bomb-making materials in his car, which had Indiana license plates.

Police sources said there was no known connection between the arrest in Santa Monica and the attack in Orlando.

ksb/jm (Reuters, AFP, AP)