MANCHESTER, England — British Prime Minister Theresa May said Tuesday night that the government had raised its terrorism threat level to critical — the highest level — meaning that another attack may be imminent even as the country mourned the victims of the Manchester bombing.
It was only the third time that Britain had raised the threat level to critical.
After a meeting of her top security officials to consider intelligence after Monday’s attack that killed 22 people and wounded dozens more at a pop concert, May said “it is a possibility we cannot ignore that there is a wider group of individuals linked to this attack.”
She added that soldiers would be deployed to assist armed police and to free some of them up to pursue the possibility that the bomber in Manchester, Salman Abedi, 22, was part of a larger cell that could be planning further attacks.
Britain’s threat level for international terrorism has for some time been at its second-highest level, indicating that an attack had been considered highly likely.
“It has now concluded, on the basis of today’s investigations, that the threat level should be increased, for the time being, from severe to critical,’’ May said in a statement. “This means that their assessment is not only that an attack remains highly likely, but that a further attack may be imminent.”
The government’s actions Tuesday night came hours after Abedi was identified by police as the bomber who carried out the assault, Britain’s deadliest terrorist attack since 2005. The explosion killed 22 people and injured 59 others at Manchester Arena.
Abedi, whose parents had emigrated from Libya and who lived in a house just 3½ miles from the arena, detonated a homemade bomb in a public concourse around 10:30 p.m. as a concert by the American pop star Ariana Grande was ending and as crowds of teenagers had begun to leave, police said. Abedi died in the attack.
At a news conference, Chief Constable Ian Hopkins of the Greater Manchester Police identified the bomber as Abedi after several news publications reported his name, but he declined to provide any further details, noting that a coroner had not yet officially identified him.
“The priority remains to establish whether he was acting alone or as part of a network,” Hopkins said.
“The work undertaken throughout the day has revealed that it is a possibility we cannot ignore that there is a wider group of individuals linked to this attack,” May said.
Abedi’s ID was found at the scene of the bombing, according to a law enforcement official, speaking on the condition of anonymity because the investigation was still underway. Abedi was born in Britain in 1994, the son of immigrants from Libya, the official said.
According to neighbors, Abedi lived with his family in a house on Elsmore Road, in the Fallowfield district. The police raided the house Tuesday afternoon, after setting off a controlled explosion to gain entry.
A neighbor, Lina Ahmed, said she knew little about the family. “They didn’t really speak to anyone,” she said. “They were nice people if you walked past.” She said the family occasionally displayed a Libyan flag outside the home.
Another neighbor, Farzana Kosur, said that the mother, who taught lessons on the Koran, had been abroad for around two months.
Also on Tuesday, police arrested a 23-year-old man outside a nearby supermarket. It was not immediately clear whether that man was connected to the attack.
The British government did not make any immediate comment on a claim by the Islamic State, which said on the social messaging app Telegram that, “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 SITE Intelligence Group, which monitors communications, also provided a translation of the claim.
As condolences poured in around the world Tuesday, Queen Elizabeth II observed a minute of silence at Buckingham Palace for the victims. The queen, her son Prince Charles, and her grandson Prince William all issued statements mourning the attack. At 6 p.m., a large crowd turned up for a vigil at Albert Square in the heart of Manchester, a city of half a million and a birthplace of the Industrial Revolution, to express grief and solidarity. Offers of support poured in; so many people volunteered to donate blood that a local blood bank had to turn people away.
The terrorist attack was the worst in the history of Manchester and northern England, and the worst in Britain since July 7, 2005, when 52 people died, along with four assailants, in coordinated attacks on London’s transit system.
Authorities reacted with horror and anger that Monday’s attack appeared to have targeted adolescents.
“After our darkest of nights, Manchester is today waking up to the most difficult of dawns,” Mayor Andy Burnham said. “These were children, young people, and their families. Those responsible chose to terrorize and kill. This was an evil act.”
President Trump phoned May from Jerusalem on Tuesday. Later, speaking at a news conference in the West Bank city of Bethlehem with Mahmoud Abbas, president of the Palestinian Authority, Trump castigated what he called the “evil losers” responsible.
The attack came in the final stretch of campaigning before a general election in Britain on June 8, and the country’s political parties agreed to suspend campaigning on Tuesday. Opposition politicians — Jeremy Corbyn of the Labour Party, Tim Farron of the Liberal Democrats, and Nicola Sturgeon of the Scottish National Party — joined May in expressing their grief and condolences.
It was unclear what effect the attack might have on the election. Some political experts suggested it would help May, who, in her previous role as home secretary, was in charge of Britain’s domestic security and is generally perceived as a tough leader. But difficult questions are being asked about what security gaps might have abetted the assault, and what could have been done to prevent it.
Grande, 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.
“I don’t think it has hit us,” said 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,” McCluskey sounded plaintive.
“We just want to go home,” she said.