MANCHESTER — Islamic State (IS) claimed responsibility yesterday for the bombing at Manchester Arena, the deadliest terrorist attack in Britain since 2005, which claimed 22 lives, left dozens injured and 59 in hospital.

The bomb tore through an entrance hall of the 21,000-seat arena at about 10.30pm on Monday (5.30am on Tuesday in Singapore) as a concert by American pop star Ariana Grande was ending and as crowds of teenagers began leaving, many for an adjacent train station.

Pandemonium ensued, as panicked adolescents struggled to find their parents and guardians waiting outside to pick them up.

As condolences poured in from around the world, the British police said that they were canvassing leads and poring over surveillance footage to determine if the assailant — who died in the assault — had acted with any accomplices. The authorities have identified 22-year-old Salman Abedi as the suicide bomber. A 23-year-old man in south Manchester was arrested as a suspected accomplice.

The British government did not make any immediate comment on the claim by IS, which said on the social messaging app Telegram: “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.”

British Prime Minister Theresa May said in a televised statement: “We now know that a single terrorist detonated his improvised explosive device near one of the exits of the venue, deliberately choosing the time and place to cause maximum carnage and to kill and injure indiscriminately.”

“The explosion coincided with the conclusion of a pop concert which was attended by many young families and groups of children,” the premier added. “This attack stands out for its appalling, sickening cowardice, deliberately targeting innocent, defenceless children and young people who should have been enjoying one of the most memorable nights of their lives.”

The terrorist strike was the worst in the history of Manchester and northern England, and the worst in Britain since 2005, when 52 people died, along with four attackers, in coordinated assault on London’s transit system.

Security experts suggested that the use of a suicide bomb in Manchester, if true, would display a level of sophistication that implied collaborators — and the possibility that other bombs had been fabricated at the same time.

“It has involved a lot of planning, it’s a bit of a step up,” said Mr Chris Phillips, a former leader of the National Counter Terrorism Security Office in Britain. “This is a much more professional-style attack,” he told the BBC.

Manchester police yesterday raided a house and carried out a controlled explosion in the south of the city centre, as part of their investigation into the bomb attack.

Mr Richard Barrett, former director of Global Counter Terrorism Operations at MI6, Britain’s foreign intelligence agency, said that the security and police forces were stretched, having to monitor more than 400 people returning from jihad in the Middle East, and 600 or so others who had tried to go but had been stopped.

“So that’s already 1,000 people,” without taking into account other sympathisers in Britain, he said.

Leaders across the world condemned Monday’s attack and offered support to Britain. President Tony Tan Keng Yam and Prime Minister Lee Hsien Loong yesterday wrote to their British counterparts to convey their condolences.

United States President Donald Trump told Mrs May yesterday that America stands with the United Kingdom. The two leaders agreed during a telephone call that the attack was “particularly wanton and depraved”.

“The president reassured the prime minister that Americans stand with the people of the United Kingdom and that our resolve will never waiver in the face of terrorism,” said the White House in a statement.

Britain is no stranger to terrorism. London suffered an attack in March, and the authorities say they have recently broken up terrorist cells. Britain’s threat level for international terrorism has for some time been at its second-highest, indicating that an attack had been considered highly likely.

Flags were flying at half-staff in Downing Street in London, where the prime minister works and lives, and at Manchester Town Hall.

British television stations showed images of girls shrieking in horror as they fled the blast area. Many parents now face the challenge of dealing with traumatised children and trying to explain an event whose senseless violence they, too, are struggling to comprehend.

Grande, an American singer who started her career as a star on a Nickelodeon TV series, expressed her sorrow on Twitter. “Broken. from the bottom of my heart, i am so so sorry. i don’t have words,” she wrote.

Mr Sadiq Khan, the mayor of London, said that the city was bolstering security measures.

Some Britons remained defiant in the aftermath of the attack.

“I don’t think it has hit us,” said Ms Jane McCluskey, of Hartlepool, England, who had attended the concert with her daughter, Charlotte. With her daughter still wearing a sweatshirt with the logo of Grande’s Dangerous Woman Tour, Ms McCluskey sounded plaintive.

“We just want to go home,” she said. AGENCIES