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An explosion rocked Manchester Arena in England at the end of a performance by the pop star Ariana Grande on Monday night.

What We Know

• At least 22 people, including children, were killed and 59 others wounded in an explosion around 10:35 p.m. on Monday in the foyer outside the main hall of the arena.

• The police said they were treating the case “as a terrorist incident.” They believe the blast came from a man who set off an “improvised explosive device” and who died in the explosion.

• The Islamic State claimed responsibility for the attack on Tuesday.

• Georgina Bethany Callander, 18, was the first victim to be identified.

• The attack is the deadliest act of terrorism in Britain since coordinated bombings on the London public transit network in 2005. The explosion also evoked memories of the November 2015 terrorist attacks in Paris, which targeted a concert hall and a soccer stadium, along with bars and restaurants.

• A 23-year-old has been arrested in South Manchester in connection with the bombing, the police’s Twitter feed announced on Tuesday.

• The Manchester Arndale shopping center was evacuated briefly on Tuesday. A man was arrested there, but the police said that he was not “currently” believed to be connected with the bombing.

• Prime Minister Theresa May spoke on Tuesday, lauding the bravery of the emergency services and of the people of Manchester. She said the police believed that they knew the identity of the assailant, but could not confirm his name. Ms. May said the attack stood out for “appalling, sickening cowardice” in the way it had targeted “defenseless children.”