MANCHESTER, England — As officials hunted for accomplices of a suicide bomber and Britain warned another attack could be imminent, thousands of people poured into the streets of Manchester in a defiant vigil Tuesday for victims of a blast at a pop concert — the latest apparent target of Islamic extremists seeking to rattle life in the West.

The attack killed at least 22 including an 8-year-old girl, shattering the revelry at a show by American singer Ariana Grande. The explosion set off a stampede of panicked concert-goers, many of them young and wearing the kitten-ear headbands popularized by Grande.

“We struggle to comprehend the warped and twisted mind that sees a room packed with young children not as a scene to cherish but as an opportunity for carnage,” British Prime Minister Theresa May said.

May said Britain’s terror-threat level had been raised to critical — meaning another attack may be imminent. The status means armed soldiers could be deployed at public events including sports matches. The threat level had been at the second-highest rung of “severe” for several years.

Islamic State claimed responsibility for the Monday attack, though a top American intelligence official said the assertion could not be verified. Manchester Police Chief Ian Hopkins identified the bomber as Salman Abedi, 22, who authorities said died in the attack. Police raided two sites in the northern English city, setting off a controlled explosion in one, and arresting a 23-year-old man in a third location.

May said Abedi was born and raised in Britain, and a European security official said he was of Libyan descent.

At least 20 heavily armed police surrounded a modest red brick house listed as Abedi’s address in a Manchester suburb on Tuesday and blasted down the door.

“It was so quick. These cars just pulled up and all these police with guns, dogs, jumped out of the car and said to us: ‘Get in the house now,’?” said Simon Turner, 46, who lives nearby.

Neighbors described Abedi as a tall, thin young man who often wore traditional Islamic dress, but few said they knew him well.

Police also searched an apartment in a nearby area that British media reported belonged to Abedi’s brother, Ismail.

Among those confirmed killed was Georgina Callander, whose death was reported by her former school.

Also killed was 8-year-old Saffie Roussos. The girl’s mother and sister were among the 59 wounded, which included at least 12 under age 16.

John Atkinson, a man in his 20s from Radcliffe, a town about 10 miles north of Manchester, was named as one of the fatalities by friends on social media and in the British press.

The bombing took place after Grande closed the show with “Dangerous Woman,” and the audience streamed toward the city’s main train station. The blast scattered bolts and other metal scraps.

“There was this massive bang. And then everyone just went really quiet. And that's when the screaming started,” said Ryan Molloy, 25. “As we came outside to Victoria Station, there were just people all over the floor covered in blood.”

The attack sparked a nightlong search for loved ones.

“I’ve called the hospitals. I’ve called all the places, the hotels where people said that children have been taken and I've called the police,” Charlotte Campbell tearfully told ITV television’s Good Morning Britain breakfast show. Campbell’s 15-year-old daughter, Olivia, had attended the show with a friend who was wounded.

“She’s not turned up,” Campbell said of her daughter. “We can’t get through to her.”

Speaking in Bethlehem in the Palestinian West Bank territory, President Donald Trump offered his “deepest condolences” to the people of Manchester and the families of the victims.

“So many young, beautiful, innocent people living and enjoying their lives murdered by evil losers in life,” he said. “I won’t call them monsters because they would like that term, they would think that’s a great name. I will call them losers because that’s what they are. They’re losers. And we’ll have more of them. But they’re losers, just remember that,” and adding, “this wicked ideology must be obliterated.”

The attack was the deadliest in Britain since four suicide bombers killed 52 London commuters in 2005.

The Washington Post contributed.