Authorities in Manchester said Tuesday that it appears that an attacker detonated an improvised explosive device at the Ariana Grande concert on Monday night, as the explosion’s death toll raised to 22.

It is not immediately clear if the unidentified man acted alone, but the person apparently died in the explosion. Police say some 400 officers were deployed overnight to help with the investigation.

Multiple law enforcement agencies are investigating the explosion, and are treating the incident as a “terror attack.”

There was panic after the explosion, which struck around 10:30 p.m. Monday night as Grande was ending the concert, part of her Dangerous Woman Tour. The singer, who was not injured, tweeted hours later: "Broken. From the bottom of my heart, I am so so sorry. I don't have words."

Labour Party leader Jeremy Corbyn says he and Prime Minister Theresa May have agreed to suspend election campaigning until further notice.

Corbyn said Tuesday he is "horrified" by the events in Manchester and that his thoughts are with the families and friends of those who have died and been injured.

Campaign events ahead of the June 8 general election will now be put on hold as Britain comes to grips with the incident and its aftermath.

May canceled campaign events Tuesday after the blast, which killed at least 22 people and injured more than 50. She is due to chair a meeting of the government's emergency committee, COBRA, later.

The Associated Press contributed to this report