NICOLA Sturgeon united with leaders around the world yesterday to express her “horror and sadness” over America’s deadliest mass shooting, which claimed 50 lives in a crowded nightclub early yesterday morning.

As police in the US said they were investigating “an act of terrorism”, the First Minister joined David Cameron, Pope Francis and French President Francois Hollande in condemning the killings.

And in a statement, US President Barack Obama said the shooting was an “act of terror” and an “act of hate” and that the FBI were investigating.

“This is a sobering reminder that attacks on any American regardless or race, ethnicity, religion or sexual orientation is an attack on all of us and the fundamental values and dignity that define us as a country,” he added.

Scottish opposition leaders Ruth Davidson and Kezia Dugdale also spoke out about the attack, which lasted three hours and which targeted people attending a popular gay venue in Orlando, Florida.

“No words can convey my horror and sadness. Just want to express heartfelt sympathy for all those affected. #Orlando,” she said in a post on Twitter.

In further statements Davidson and Dugdale said they stood behind the LGBT community.

The Scottish Conservative leader tweeted: “News from #Orlando is shocking – people from all around the world stand with the LGBTQ community today.”

While the Scottish Labour leader said: “The scenes from Orlando are utterly heartbreaking. The thoughts of everyone in Scotland will be with those who have been killed, their families and friends. This looks to have been an attack on the very freedom to love who you want to love. We stand in solidarity with the entire LGBT community and the vast majority of Americans who will oppose this hate.”

While people in Florida queued to give blood and the debate around US gun control reopened, police revealed a gunman – later identified as Omar Mateen – wielding an assault-type rifle, a handgun and “some kind of device” strapped to his body opened fire inside the Pulse nightclub about 2am local time.

As the shooting began staff at the venue, which had been hosting a Latin-themed night, posted on Facebook: “Everyone get out of pulse and keep running”.

Mateen, 29, from Fort Pierce, a city about two hours drive south of Orlando, in St Lucie County, was shot dead in a gun fight with police, at about 5am, who had stormed the building to rescue hostages.

An FBI spokesman said the suspect appeared to “have leanings towards” radical Islamist ideology but it was not yet clear whether this was a case of domestic or international terrorism.

A report from one US broadcaster said yesterday Mateen called 911, the emergency number, before the attack and when the operator answered, “swore his allegiance to [Abu Bakr al-]Baghdadi”, the leader of terror group Daesh.

The identities of the victims and the number of casualties were still emerging yesterday, but by late afternoon police confirmed 50 people had died and more than 53 injured and taken to hospital. Many of those hurt were critically injured.

“There’s blood everywhere,” Orlando mayor Buddy Dyer said.

Jackie Smith, who was inside the club, said two friends next to her were shot.

“Some guy walked in and started shooting everybody. He had an automatic rifle, so nobody stood a chance,” Smith said. “I just tried to get out of there.”

“This is an incident, as I see it, that we certainly classify as ‘domestic terror incident’,” Orange County Sheriff Jerry Demings said.

FBI agent Ron Hopper said there was no further threat to Orlando or the surrounding area.

When asked if the gunman had a connection to radical Islamic groups, Hopper said authorities had “suggestions that individual has leanings towards that”.

Mateen’s father Mir Seddique told NBC News his son may have carried out the attack after he saw a gay couple kissing in Miami.

The BBC reported last night that Mateen was not on a terrorism watch list, although was being investigated for an unrelated criminal act.

A woman who was outside the dance club early on Sunday was trying to contact her 30-year-old son, Eddie, who texted her when the shooting happened and asked her to call police.

He told her he ran into a toilet with other club patrons to hide. He then texted her: “He’s coming.”

“The next text then said: ‘He has us, and he’s in here with us’,” Mina Justice said.

“That was the last conversation.”