Suspected suicide bomber Salman Abedi killed 22 people and himself at an Ariana Grande concert in Manchester, England. At least 59 people were injured.

The blast took place at the end of the singer’s set, sending concertgoers into a panic. The audience was filled with young children and their parents.

U.K. authorities are treating the explosion as terrorism. Police arrested a 23-year-old man in connection with the investigation.

ISIS on Tuesday claimed responsibility for the attack.

Moments after Ariana Grande finished performing her 2016 hit single “Dangerous Woman” Monday, a loud blast jarred thousands of British fans cheering the American pop star at the Manchester Arena.

Concertgoers, many of them Grande’s young fans and their friends, parents and grandparents, scrambled to evacuate the enormous concert hall, filling the arena with screams. Some were still clutching pink balloons that had dropped from the rafters during Grande’s encore.

At least 22 people were killed, including children, and 59 were injured in the late-night explosion, police said. Twelve children under the age of 16 were among the wounded. Two of the victims have been identified as 18-year-old Georgina Callander and 8-year-old Saffie Rose Roussos.

Manchester police have identified 22-year-old Salman Abedi, a British national whose parents came to the U.K. from Libya, as the attacker. They previously said the blast would be “treated as a terrorist incident until police know otherwise.”

The Islamic State militant group claimed responsibility in a statement released on Tuesday for the attack via one its official media channels. It is unclear, however, whether ISIS had any direct role in planning the Manchester bombing or if the attacker was in communication with the group. The U.S. has not verified that ISIS was behind the attack, Director of National Intelligence Dan Coats said Tuesday morning.

Manchester Chief Constable Ian Hopkins said early Tuesday the attack was conducted by one man who died at the scene. Initial reports said he carried an improvised explosive device near the arena and detonated.

“We have been treating this as a terrorist incident and we believe that while the attack last night was conducted by one man, the priority is to establish whether he was acting alone or as part of a network,” Hopkins said.

Christopher Furlong via Getty Images The blast took place outside the famous concert hall, the largest indoor arena in Europe, near the box office, just after the show ended.

Authorities in Manchester said they arrested a 23-year-old man as part of their investigation into the attack.

British Prime Minister Theresa May at a Tuesday press conference called the explosion “a callous terror attack” and said it was “among the worst terrorist incidents we have ever experienced in the United Kingdom.”

“This attack stands out for its appalling, sickening cowardice, deliberately targeting innocent, defenseless children and young people,” she said.

Manchester held a mass vigil on Tuesday night for victims of the attack, with a large crowd of mourners gathering outside of town hall to pay respect.

The blast took place outside Manchester Arena, the largest indoor arena in Europe, near the box office, just after the show ended. Many parents were awaiting their children outside to take them home after the sold-out show.

Manchester Arena is one of Europe’s largest with a capacity of 21,000 (in comparison, New York City’s Madison Square Garden can seat around 20,000 depending on the event). Since it opened in 1995, it has hosted popular international sporting events, comedy shows and concerts, including American acts like Chris Rock, Madonna and Lady Gaga, as well as British groups Oasis, The Verve and The Charlatans.

Dave Thompson via Getty Images Monday’s blast comes at a turbulent time for the U.K. Britain is on its second-highest alert level of “severe,” meaning an attack by militants is considered highly likely.

Among those struck in the mayhem was Andy Holey, who was picking up his wife and daughter from the concert.

“As I was waiting, an explosion went off and it threw me about 30 feet from one set of doors to the other set of doors,” Holey told BBC. “When I got up I saw bodies lying on the ground. My first thought was to go into the arena to try to find my family.”

Holey said he “looked through some of the bodies to try and find my wife and daughter,” and eventually found them unharmed.

Elena Semino of Lancaster shared a similar story with The Guardian. Semino and her husband were waiting near the box office to pick up their 17-year-old daughter when the explosion occurred.

“My husband and I were standing against the wall, luckily, and all of a sudden there was this thing. I can’t even describe it,” Semino said. “There was this heat on my neck, and when I looked up, there were bodies everywhere.”

Inside the arena, concertgoers scrambled to evacuate amid screaming.

EXPLOSION AT MANCHESTER ARENA AND EVERYONE RAN OUT SO SCARY😭 pic.twitter.com/pJbUBoELtE — ♡♡ (@hannawwh) May 22, 2017

Witnesses described a chaotic scene, with many people confused about what just had happened.

“There were just a loud bang and a flash and everyone tried to scramble out,” Jade Baynes, 18, told the Guardian. “An alarm came on telling everyone to stay calm, but leave as quickly as possible.”

“You could feel it in your chest,” Catherine Macfarlane told Reuters news agency. “It was chaotic. Everybody was running and screaming and just trying to get out.”

Moments earlier, fans were enjoying Grande’s performance, one of four stops on the U.K. leg of her “Dangerous Woman” tour. The tour has been suspended indefinitely following the attack.

i took this minutes before the explosion. the best night of my life has turned to the worst. #Manchester #Manchesterarena #DWTManchester pic.twitter.com/v1QQaZVWTS — pray for manchester (@lnandelrey) May 22, 2017

Grande was unharmed, her publicist told The New York Times. She later tweeted her condolences to her fans:

broken.

from the bottom of my heart, i am so so sorry. i don't have words. — Ariana Grande (@ArianaGrande) May 23, 2017

Grande got her start on Nickelodeon’s “Victorious” and later starred on its spinoff “Sam & Cat.” Her debut album, “Yours Truly” was released in 2013 and featured early hits “Baby I” and “Right There.” Grande has since released two more records and cemented herself as one of the reigning pop divas of her time.

The 23-year-old is a four-time Kids’ Choice Award-winner and because of her roots on Nickelodeon, her fan-base tends to skew on the younger side. Witnesses said the audience included many children.

Celebrities flooded Twitter on Thursday with condolences for the victims of the blast.

Tearing up imagining innocent concert goers losing their lives.. praying for everyone and all #arianators. 🙏🏼🙏🏼🙏🏼 — Demi Lovato (@ddlovato) May 22, 2017

My thoughts and prayers go out to everyone affected in Manchester. — Selena Gomez (@selenagomez) May 23, 2017

Britain’s leaders, including Labor leader Jeremy Corbyn, responded with solemn statements throughout the night.

Terrible incident in Manchester. My thoughts are with all those affected and our brilliant emergency services. — Jeremy Corbyn (@jeremycorbyn) May 22, 2017

Manchester’s mayor, Andy Burnham, called the attack, “an evil act.”

“Manchester will stand strong and stand together,” he said.

Manchester mayor Andy Burnham: "This was an evil act" pic.twitter.com/YDoGjg8c7x — BuzzFeed UK (@BuzzFeedUK) May 23, 2017

London stands with Manchester, London Mayor Sadiq Khan tweeted.

London stands with Manchester - our thoughts are with all those killed and injured tonight and our brave emergency services. https://t.co/0al1LzXvXE — Sadiq Khan (@SadiqKhan) May 22, 2017

President Donald Trump said that the attack was the work of “evil losers.”

“I won’t call them monsters, because they would like that term ... they’re losers, just remember that,” he said Tuesday during a press conference with Palestinian President Mahmoud Abbas. Trump met with Abbas while on his first foreign trip as president.

The U.S. Department of Homeland Security said it was monitoring the situation, but had “no information to indicate a specific credible threat involving music venues in the United States.”

First lady Melania Trump tweeted sympathies for the victims.

My thoughts and prayers to the families of #Manchester. — Melania Trump (@FLOTUS) May 23, 2017

Leaders in France, which is still under a state of emergency after the 2015 and 2016 attacks in Paris and Nice, expressed solidarity.

“We stand together in the fight against terrorism,” French President Emmanuel Macron said in a tweet.

J'adresse mes pensées au peuple britannique, aux victimes et à leurs proches. Nous menons ensemble le combat contre le terrorisme. — Emmanuel Macron (@EmmanuelMacron) May 23, 2017

Monday’s blast comes at a turbulent time for the U.K. Britain is on its second-highest alert level of “severe,” meaning an attack by militants is considered highly likely.

It’s been just two months since a 52-year-old British citizen ran down pedestrians with a vehicle on Westminster Bridge and stabbed a police officer to death before being killed by authorities. Five people, including the attacker and the officer were killed, and more than 40 were injured.

And at the start of next month, Brits are headed to the polls to vote in early elections. May is hoping to strengthen her coalition ahead of talks to exit the European Union. Politicians have agreed to suspend campaigning in the wake of the attack.

Chris D’Angelo, Stephanie Marcus, Jesselyn Cook, Nick Robins-Early and Reuters contributed reporting.

Darren Staples / Reuters A man writes a message on the pavement in central Manchester.

Christopher Furlong via Getty Images Armed police patrol on Shudehill walking past the first floral tributes to the victims of the terrorist attack in Manchester, England.

Anadolu Agency via Getty Images Vikki Baker and her thirteen year old daughter Charlotte hug outside the Manchester Arena.

Anadolu Agency via Getty Images People react as they leave the Park Inn hotel that took in victims from the Manchester Arena.

Christopher Furlong via Getty Images Crowds of people wait outside after police evacuated the Arndale Centre in Manchester.

BEN STANSALL via Getty Images Retail staff hug each other after being evacuated from the Arndale Centre shopping mall in Manchester.

OLI SCARFF via Getty Images A girl wearing a t-shirt of US singer Ariana Grande carrying balloons from the Ariana Grande concert at the Manchester Arena.

Jeff J Mitchell via Getty Images Messages are left amongst tributes by members of the public in St Ann Square on Tuesday, May 23, 2017 in Manchester.

OLI SCARFF via Getty Images A floral tribute and a teddy bear are pictured alongside police tape near to the Manchester Arena.

Joel Goodman/LNP Police and other emergency services assist a victim near the Manchester arena.

Andrew Yates / Reuters Two women wrapped in thermal blankets stand near the Manchester Arena.

Press Association Armed police at Manchester Arena after reports of an explosion at the venue.

Dave Thompson via Getty Images Members of the public are escorted from the Manchester Arena.

Press Association Armed police at Manchester Arena after reports of an explosion at the Manchester Arena during an Ariana Grande concert.

Dave Thompson via Getty Images Members of the public receive treatment from emergency service staff at Victoria Railway Station.

Stringer . / Reuters Concert goers react after fleeing the Manchester Arena.

Stringer . / Reuters A police van and an ambulance are seen outside the Manchester Arena.

Dave Thompson via Getty Images Police stand by a cordoned off street close to the Manchester Arena.

Press Association Emergency services at Manchester Arena.

Press Association Emergency services at Manchester Arena after reports of an explosion at the venue during an Ariana Grande gig.

Dave Thompson via Getty Images A policeman patrols Victoria Railway Station close to the Manchester Arena on May 23, 2017 in Manchester, England.

Andrew Yates / Reuters Vehicles are seen near a police cordon outside the Manchester Arena.

Stringer . / Reuters Police vehicles are seen outside the Manchester Arena.

PAUL ELLIS via Getty Images Medics and rescuers in Manchester.

CORRECTION: This article previously misstated Callander’s age as 16; she was 18.