MercoPress. South Atlantic News Agency

Obama describes the killings as “an act of terror and an act of hate”

Americans were united in “grief, outrage and resolve to defend our people”, said president Obama who ordered flags flown at half mast until next Thursday sunset.

US President Barack Obama has described Sunday morning's gun attack on a gay nightclub in Orlando, Florida, as “an act of terror and an act of hate”. Americans were united in “grief, outrage and resolve to defend our people”, he said.Omar Mateen, 29, killed 50 people and wounded 53 at the Pulse club before being shot dead by police.

The so-called Islamic State group has said it was behind the attack, but the extent of its involvement is not clear. A statement on its affiliated Amaq news agency said that an IS “fighter” was responsible.

NBC News reported that Mateen had called the emergency services before the attack and swore allegiance to IS. The gunman was killed in an exchange of fire with 11 police officers, after taking hostages at the club.

The attack is the worst mass shooting in recent US history. A moment of silence was observed across the US at 18:00 local time (22:00 GMT).

In an apparently unrelated event, a heavily armed man was held on weapons and explosive materials charges in southern California after saying he wanted to go to a gay pride event in Los Angeles.

President Obama said the “brutal murder of dozens of innocent people” was a further reminder of how easy it was to acquire a deadly weapon in the US and shoot people.

“We have to decide if that's the kind of country we want to be,” said the president, who has campaigned for stricter gun laws. “To actively do nothing is a decision as well.” He added that it was a heartbreaking day for the LGBT community, and that an attack on any American was an attack on all.

Obama has ordered flags on federal buildings to be flown at half mast until sunset on Thursday. Later the White House said Obama had postponed a joint appearance with the Democratic Party's presumptive nominee for president, Hillary Clinton.

Mrs. Clinton said in a statement: “This reminds us once more that weapons of war have no place on our streets.”

And in a message to LGBT (lesbian, gay, bisexual and transgender) people, she said: “We will keep fighting for your right to live freely, openly and without fear. Hate has absolutely no place in America.”

Meanwhile her Republican rival, Donald Trump, said Obama should step down for refusing to use the words “radical Islam” when condemning the attack. “If we do not get tough and smart real fast, we are not going to have a country anymore,” he said.

The head of the Council on American-Islamic Relations urged politicians not to “score points” or “exploit fear” in the aftermath of the attack.

In a direct message to IS, Nihad Awad said: “You do not speak for us. You do not represent us. You are an aberration.”

Mateen, a US citizen of Afghan descent who was born in New York and lived in Florida, was not on a terrorism watch list. However, officials revealed that the FBI had twice interviewed him in 2013-14 after he made “inflammatory remarks” to a colleague, before closing their investigation.

It has emerged that he legally purchased several guns in the past few days. Mateen worked for a private security company. His employers, G4S, said he had worked for them for nine years and carried a gun as part of his job.

In a statement, the company said he had undergone screening twice, in 2007 and 2013, and the checks had not revealed anything of concern.

His ex-wife, Sitora Yusufiy, said he was “unstable”, had a violent temper and beat her up regularly during their short-lived marriage for trivial things like not doing laundry.