The Daesh (ISIL) terrorist group has taken responsibility for Monday night's attack at the Manchester Arena that killed 22 people, including children, and wounded 59 others.
"One of the soldiers of the Caliphate was able to place an explosive device within a gathering of the Crusaders in the city of Manchester," the group said in a statement Tuesday.
Daesh did not publish a name or picture of the attacker, which they have previously done for some major attacks they claimed responsibility for.
A suicide bomber with an “improvised” explosion device targeted a concert arena in Manchester as thousands of young people streamed from the venue.
Police identified the suspected bomber as Salman Abedi, aged 23, and said they were trying to establish whether he had acted alone or with help from others.
"Our priority, along with the police counter-terrorism network and our security partners, is to continue to establish whether he was acting alone or working as part of a wider network," Manchester Police Chief Constable Ian Hopkins said.
Two American officials who have been in contact with British authorities said the attacker was believed to have traveled to Manchester from London by train.
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British Prime Minister Theresa May condemned the attack as “among the worst terrorism” in the United Kingdom.
“All acts of terrorism are cowardly attacks on innocent people, but this attack stands out for its appalling, sickening cowardice,” May said in a statement outside Downing Street on Tuesday.
“We struggle to comprehend the warped and twisted mind that sees a room of young people as an opportunity for carnage.”
She also described the terrorist incident as “the worst ever to hit the north of England.”
The statement came as British police said that they had arrested a man in Chorlton in connection with the deadly attack.
Andrew Parker, director general of MI5, said the attack was “disgusting,” adding that the security service remained “relentlessly focused, in numerous current operations” to combat the “surge of terrorism” in the UK.
The first victim of the attack has been identified as 18-year-old student Georgina Callander. The teenager was one of the first people to be transported to hospital, but she later died with her mother at her bedside.
Relatives are using social media to get information on their loved ones, and an emergency number has also been established.
London Mayor Sadiq Khan said more police officers had been ordered to beef up security in the British capital.
The incident was the worst terrorist attack in Britain since the July 7, 2005 bombings in central London, which killed 52 people.
Election campaigning suspended
Opposition Labour leader Jeremy Corbyn paid tribute to the victims of the Manchester blast.
“I am horrified by the horrendous events in Manchester last night. My thoughts are with families and friends of those who have died and been injured,” he said in a statement. “Today the whole country will grieve for the people who have lost their lives.”
Corbyn said he had spoken with Prime Minister May and both had agreed to suspend their campaigning in the upcoming general election until further notice.
Other political parties also suspended their campaigning in the wake of the attack.
Royal Family filled with 'intense sadness'
The Royal Family also expressed shock over “this act of barbarity” in Manchester.
In a statement published on the Royal Family's official website, Queen Elizabeth II condemned the "dreadful event" and thanked the emergency services for handling the situation.
“The whole nation has been shocked by the death and injury in Manchester last night of so many people, adults and children, who had just been enjoying a concert,” the Queen said.
“I know I speak for everyone in expressing my deepest sympathy to all who have been affected by this dreadful event and especially to the families and friends of those who have died or were injured,” she added.
“I want to thank all the members of the emergency services, who have responded with such professionalism and care,” she stated.
Prince Charles also expressed his deep distress.
“My wife and I were so profoundly shocked to learn of the truly dreadful event which took place in Manchester last night,” he said in a statement.
“That such a large number of people, including so many young concert-goers, lost their lives or have suffered so much in this appalling atrocity is deeply distressing and fills us with intense sadness.”
'Wicked ideology'
US President Donald Trump, who is currently on a Middle East tour, said Tuesday “evil losers” were behind Monday’s attack.
“I extend my deepest condolences to those so terribly injured in this terrorist attack and to the many killed and the families – so many families of the victims,” Trump said.
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“This wicked ideology must be obliterated – and I mean completely obliterated – and the innocent life must be protected. All civilized nations must join together to protect human life and the sacred right of our citizens to live in safety and in peace,” the president said.
Secretary of State Rex Tillerson said the American authorities were “working closely” with British officials to help them investigate the attack.
The US Director of National Intelligence Dan Coats, who has just returned from London, said he had discussed security threats facing both nations with British intelligence officials.
However, Coats said the US intelligence agencies “have not verified, yet, the connection” between Daesh and the Manchester bombing.
“It once again reminds us. This threat is real. It is not going away and needs significant attention to do everything we can do to protect our people,” Coats told a congressional committee on Tuesday.