ISIS claimed responsibility for Monday's deadly attack at the Manchester Arena and said it was carried out with an explosive device planted at the concert, according to a statement the group posted on Telegram.

"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 statement said.

At least 22 people, including some children, were killed and 59 were wounded when a suicide bomber struck as thousands of fans streamed out of a concert by US singer Ariana Grande in the English city of Manchester on Monday.

British police said the incident, in which at least 59 people were injured, was being treated as a terrorist incident. Police carried out a controlled explosion on a suspect device several hours after the blast.

Police said they responded to reports of an explosion shortly after 10:35 pm (2135 GMT) at the arena, which has a capacity for 21,000 people, and where the US singer had been performing to an audience that included many children.

Latest statement on incident at Manchester Arena pic.twitter.com/BEpLOan3dY

— G M Police (@gmpolice) May 23, 2017

If confirmed as a terrorism incident, it would be the deadliest attack in Britain by militants since four British Muslims killed 52 people in suicide bombings on London's transport system in July 2005.

The blast also came two and half weeks ahead of an election in which Prime Minister Theresa May is predicted by opinion polls to win a large majority.

"We were making our way out and when we were right by the door there was a massive explosion and everybody was screaming," concert-goer Catherine Macfarlane told Reuters.

"It was a huge explosion -- you could feel it in your chest. It was chaotic. Everybody was running and screaming and just trying to get out."

#ManchesterVic - Manchester Victoria station has been evacuated and trains are unable to run.

— National Rail (@nationalrailenq) May 22, 2017

It has been reported that after hearing a loud bang at the end of the concert people rushed toward the exit, creating a chaotic scene at Manchester' Victoria Station.

WATCH: People running inside Manchester's Victoria Station after blast reported following Ariana Grande concert: https://t.co/rDbaf5SDzQ pic.twitter.com/7unoW0WBxw

— Good Morning America (@GMA) May 22, 2017

Manchester Arena, the largest indoor arena in Europe, opened in 1995 and is a popular concert and sporting venue.

A spokesman for Ariana Grande's record label said that the singer was "okay". A video posted on Twitter showed fans screaming and running out of the venue.

Britain is on its second-highest alert level of "severe" meaning an attack by militants is considered highly likely.

British counter-terrorism police have said they are making on average an arrest every day in connection with suspected terrorism.

In March, a British-born convert to Islam plowed a car into pedestrians on London's Westminster Bridge, killing four people, before stabbing to death a police officer who was on the grounds of parliament. He was shot dead at the scene.

Politicians statements on the horrific blast:

British Prime Minister Theresa May said on Tuesday that authorities were working to establish the details of the blast, adding that it was being treated as an "appalling terrorist attack".

"We are working to establish the full details of what is being treated by the police as an appalling terrorist attack," she said in a statement.

"All our thoughts are with the victims and the families of those who have been affected."

Canadian Prime Minister Justin Trudeau tweeted:

Canadians are shocked by the news of the horrific attack in Manchester tonight. Please keep the victims & their families in your thoughts.

— Justin Trudeau (@JustinTrudeau) May 23, 2017

British Liberal Democrat leader Tim Farron also tweeted a message.

My deepest condolences to the victims and families in Manchester. As always our emergency services have shown great bravery and heroism.

— Tim Farron (@timfarron) May 22, 2017

US House of Representatives Speaker Paul Ryan stated that he is "praying for the victims and their families".

Young and innocent lives lost in #Manchester tonight. Praying for the victims and their families.

— Paul Ryan (@SpeakerRyan) May 23, 2017

Labour Party leader Jeremy Corbyn said, "My thoughts are with all those affected and our brilliant emergency services."

Terrible incident in Manchester. My thoughts are with all those affected and our brilliant emergency services.

— Jeremy Corbyn (@jeremycorbyn) May 22, 2017

Ariana Grande tweeted

Pop star Ariana Grande said on Monday she was "broken" five hours after a bombing killed 19 people and wounded dozens of others at her concert in Manchester, England.

Making her first comment since an explosion detonated just outside Manchester Arena at the end of her performance there, Grande said on Twitter: "broken. from the bottom of my heart, i am so so sorry. i don't have words."

Representatives for Grande have said that the 23-year-old pop star was physically "okay" following the blast, which British authorities say was being treated as a terrorist attack.

broken.
from the bottom of my heart, i am so so sorry. i don't have words.

— Ariana Grande (@ArianaGrande) May 23, 2017

ISIS supporters celebrate the attack

Islamic State supporters celebrated on social media on Tuesday after a blast at a concert venue in the north of England killed at least 19 people, although the militant Islamist group has not formally claimed responsibility.

Twitter accounts affiliated to Islamic State have used hashtags referring to the blast to post celebratory messages, with some users encouraging similar attacks elsewhere.

Some messages described the attack as an act of revenge in response to air strikes in Iraq and Syria.

"It seems that bombs of the British airforce over children of Mosul and Raqqa has just came back to #Manchester," one user named Abdul Haqq said on Twitter, in reference to the Iraqi and Syrian cities held by the militants where a U.S.-led coalition, of which Britain is a member, is conducting air strikes.

Supporters posted messages encouraging each other to carry out "lone wolf" attacks in the West and shared Islamic State videos threatening the United States and Europe.

One user said he hoped Islamic State was responsible for the attack, although no claim has appeared on any of the militant's group's official social media channels.

"We hope that the perpetrator is one of the soldiers of the caliphate," he wrote on a channel affiliated to the group hosted by messaging network Telegram.

Others posted banners saying "the beginning is in Brussels and Paris, and in London we form a state," in reference to previous similar "lone wolf" attacks in Belgium and France for which the group has claimed responsibility.