■ The Islamic State claimed responsibility for a bombing Monday night in the foyer outside the main hall of the Manchester Arena that killed 22 people and wounded 59 others. View photos from the aftermath of the attack.

■ Children and teenagers who were attending a concert by the American pop star Ariana Grande were among the dead, the police said. An 18-year-old student and an 8-year-old girl were confirmed killed in the bombing. Ms. Grande was not hurt.

■ The police say a man detonated an “improvised explosive device” and died at the scene. Investigators say they believe the man acted alone, but they are investigating whether he was part of a wider network.

■ Prime Minister Theresa May described the episode as “an appalling terrorist attack,” and said law enforcement officers believed they knew the identity of the attacker, but were not ready to confirm his name.

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What We Don’t Yet Know

The police have not released the identity of the bomber, nor have they commented on the motive of the assailant. It is also not clear whether he received help and whether he intended to kill himself.

The Islamic State claimed responsibility for the attack, identifying the bomber in its statement as a “soldier of the caliphate,” but the extent of the militant group’s connection is unclear.

We are also trying to find out:

■ How many of the 22 victims were children.

■ What gaps in security at the arena might have abetted the attack, and what could have been done to prevent it.

■ What effect the attack might have on the June 8 general election. Britain’s leading political parties agreed to suspend campaigning out of respect for the victims of the attack.

For the latest on the Manchester attack and other major news, sign up for our Morning Briefing newsletter.

First Victims Are Identified

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Saffie Rose Roussos, an 8-year-old from Lancashire in northwest England, was attending the Ariane Grande concert with her mother and older sister, the Lancashire County Council said on Tuesday. Saffie was killed in the attack. News reports said her mother and her sister, who is in her 20s, were being treated at a hospital for their injuries.

The principal of Tarleton Community Primary School, which Saffie attended, said she was a “beautiful little girl,” who was “quiet and unassuming, with a creative flair.” The principal, Chris Upton, said that news of Saffie’s death had been a “tremendous shock.”

Earlier, Georgina Bethany Callander, an 18-year-old health and social care student, was the first victim of the Manchester attack to be identified on Tuesday. News reports said she had died with her mother at her bedside.

Read more about the victims who have been identified here.

Others in Manchester were still appealing for help locating loved ones who had attended the concert.

We have still not found OLIVIA CAMPBELL. If you see her please contact me ASAP. pic.twitter.com/8LboKg0B2n

— Aleshia Anne (@Hello_Leesha) May 23, 2017

The soccer club Manchester City has opened part of its Etihad Stadium to be used as an emergency facility for families awaiting news of relatives still unaccounted for. Representatives of the Greater Manchester Police and the city council were on hand Tuesday, helping to direct inquiries.

Volunteers looking to help were also directed to the stadium, about a mile east of the Manchester Arena. A number of local shops have sent food and supplies to the families waiting there.

— Dan Bilefsky, Philip Pan and Rory Smith

Theresa May Pledges British Way of Life Will ‘Prevail’

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Speaking outside her Downing Street office on Tuesday, the British prime minister appealed for anyone with information about the bombing to come forward, and she vowed that Britain’s way of life would “always prevail.”

“Let us remember those who died, and let us celebrate those who helped, safe in the knowledge that the terrorists will never win,” she said in comments broadcast on television.

Mrs. May said the attack Monday evening “stands out for its appalling, sickening cowardice — deliberately targeting innocent, defenseless children and young people who should have been enjoying one of the most memorable nights of their lives.”

— Sewell Chan and Prashant S. Rao

Queen Offers Her Condolences

In a statement on Tuesday, Queen Elizabeth II offered her “deepest sympathy to all who have been affected by this dreadful event.”

“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,” she said.

Prince Charles also issued a statement of condolence.

— Prashant S. Rao

Trump Condemns ‘Horrible Morning of Death’

President Trump condemned the bombing as a “very horrible morning of death,” and pledged “absolute solidarity” with Britain.

Speaking in Bethlehem, in the West Bank, while on his first foreign trip as president, Mr. Trump said the bombing underscored the message that he had delivered over the past several days about the need to confront the threat of terrorism.

“The terrorists and extremists, and those who give them aid and comfort, must be driven out from our society forever,” Mr. Trump said after a meeting with Mahmoud Abbas, the president of the Palestinian Authority. “This wicked ideology must be obliterated, and I mean completely obliterated.”

‘Everyone Started Crying and Screaming’

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By K.K. Rebecca Lai, Jugal Patel and Karen Yourish | Satellite image via Google Earth

Laura Bruce, 18, was with her 25-year-old sister, Amy, in one of the arena’s upper tiers when they heard the explosion. “Everyone below us just turned and ran,” she said. “Because we were higher up, we could not get out for five minutes. When we came out, a man walked past us just covered in blood.”

Sophie Tedd, 25, had traveled from Darlington, England, to attend the concert with her friend Jessica Holmes. At the end of the concert, they heard a loud bang and initially wondered whether “a speaker had blown.”

Video from inside the arena showed a surreal scene of people scrambling for the exits amid pink balloons. The balloons were part of choreographed staging for Ms. Grande’s tour, after a segment with projections and lasers.

— Rory Smith and Ben Sisario

False Reports Quickly Circulate

Hours after the deadly attack in Manchester, false reports about the assailant and victims started to circulate across social media, often aided by Britain’s traditional news media.

Two of the country’s newspapers reported incorrectly that a gunman had been spotted near a hospital on the outskirts of the city in northern England. The local authorities quickly debunked that report through a tweet.

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As in previous attacks across Europe, including those recently in France and Germany, false reports of people looking for victims of the attack also spread rapidly, racking up thousands of likes and retweets even though the information was incorrect.

Other posts included photographs of Ms. Grande, portraying her — falsely — in the aftermath of the blast.

— Mark Scott

The Terrorism Threat in Britain

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The attack at the arena was the worst terrorist attack in Britain since the 2005 bombings of London’s buses and subway, which killed 52 people.

British authorities, who say they have foiled numerous terrorist plots, have maintained the nation’s threat level, set by MI5, the domestic intelligence service, at “severe,” the second-highest level, for months. That means the authorities considered an attack “highly likely.” And counterterrorism officials have been warning that as the Islamic State comes under more military pressure in Iraq and Syria, it will try to strike abroad.

— Steven Erlanger

Blast Came After ISIS Plea

Last week, the Islamic State released a 44-minute video featuring fighters of different nationalities, enjoining their supporters back home to carry out acts of violence. Among them was a man identified as a British national, according to a translation of the video provided by the Middle East Media Research Institute, which tracks jihadi propaganda.

Besides the threat last week, the Islamic State has repeatedly targeted Britain in its propaganda, though with little visible effect until earlier this year.

— Rukmini Callimachi

Who Is Ariana Grande?

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Ms. Grande said after the attack that she was “broken.” She wrote on Twitter how sorry she was for the fans who were killed and injured in the bombing.

The 23-year-old singer and actress began her career on the children’s television network Nickelodeon. She played the character Cat Valentine — whom she once described as “simple” — on the hit shows “Victorious” and “Sam & Cat.”

Ms. Grande has written in a Facebook post that playing Cat Valentine had helped her transition “from teenager to adult.”

The concert that was attacked on Monday was part of a tour to support Ms. Grande’s 2016 album, “Dangerous Woman.” Reviewing the tour’s February stop at Madison Square Garden, the New York Times music critic Jon Pareles called Ms. Grande’s performance “a show of confidence, prowess and aplomb.”

— Mike Ives

Reaction From Other Music Stars

Arena Largest Such Venue in Britain

The Manchester Arena is the largest indoor venue in Britain, with a capacity of 21,000, or 18,000 for concerts. It was constructed as part of Manchester’s bid to host the Olympic Games in 1996 and 2000. The venue is connected to the Manchester Victoria Station, which remained closed on Tuesday.

The Pennsylvania-based company SMG manages the arena, and Wes Westley, the president and chief executive of the company, described the precautions at the venue.

“It is obviously as tight security as anywhere in the states,” he said in an interview. “Backpacks are not allowed. Drinks are taken away from people. You have to go through very strict security to enter the arena.”

He explained that attendees arrive through a large public foyer, which is where the explosion occurred. The area is often where parents wait for their children after concerts.

— Ben Sisario and Gerry Mullany

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