U.K. Prime Minister Theresa May said Tuesday the threat level in the region has been raised from severe to critical after Monday's attack in Manchester, England.

Critical is the highest of the country's five threat levels. Soldiers will now be deployed at public events, and police officers responsible for guarding key sites will be replaced by armed military officers.

The change indicates that another attack may be imminent.

May said the U.K. could not ignore the possibility that more individuals are linked to the Manchester Arena attack.

The man suspected of carrying out the explosion, at an Ariana Grande concert, was identified as 22-year-old Salman Abedi, police said today. At least 22 people died from the blast, and dozens more were injured.

Abedi died at the scene after using an improvised explosive device, officials said. Police are still trying to determine if he acted alone or was part of a group.

A photo of Abedi was first published on the front page of the British newspaper The Sun.

PHOTO: The cover of the May 24, 2017 issue of the British newspaper The Sun, features a photo of suspected attacker Salman Abedi. (The Sun) More

PHOTO: An armed police officer stands outside a residential property near to where a man was arrested in the Chorlton area of Manchester, England, May 23, 2017. (Stefan Wermuth/Reuters) More

The suspect was originally identified as a 23-year-old male, according to a source; police have since said he was 22.

A 23-year-old man has been arrested in South Manchester in connection with the attack, police said. Police also said authorities executed two warrants as part of the investigation: one in the Whalley Range district of Manchester and one in the Manchester suburb of Fallowfield, where a controlled explosion took place.

Greater Manchester Police are requesting dashcam footage from "anyone who was in Manchester city centre" between 8 p.m. and 11 p.m. Monday as part of its investigation.

A 39-year-old man was also arrested in Birmingham today near a vigil for the attack. The man is "known to police and is thought to have a history of mental ill-health," Birmingham police said in a statement. A small ax and large stick were recovered at the vigil, police said.

ISIS has claimed responsibility for the explosion. In a statement translated from Arabic, ISIS said that a "soldier of the caliphate" placed explosives at a gathering of "crusaders" — meaning Christians — at the Manchester Arena. The statement said about 30 people were killed and about 70 more were wounded.

PHOTO: Crowds of people wait outside after police evacuated the Arndale Centre, May 23, 2017, in Manchester, England. (Christopher Furlong/Getty Images) More

The explosion is being treated as a terrorist attack.

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Greater Manchester Police said officers were called to the Manchester Arena just before 10:35 p.m. local time on Monday. The explosion happened near the arena's foyer after the concert, according to witnesses, who reported hearing a bang as they exited.

An 8-year-old girl named Saffie Rose Roussos was among those killed.

PHOTO: An undated photo of 8-year-old Saffie Roussos; she died in the Manchester, England, attack on May 22, 2017. (SWNS.com) More

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