At least 22 people are dead following an explosion outside a concert at Manchester Arena in England, the Greater Manchester Police said Monday.

At a press conference late Monday, Great Manchester Police Chief Constable Ian Hopkins said authorities are working with national agencies and intelligence officials following the incident.

He said police are "are currently treating this as a terrorist incident until we have further information" and said authorities are coordinating with "national counter terrorism policing network and UK intelligence partners."

The explosion was first reported at 10:33 p.m. at the end of an Ariana Grande concert.

Ariana Grande tweeted hours after her concert that she was "broken." "From the bottom of my heart, I am so so sorry," she said. "I don't have words."

broken.

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

CBS News said it confirmed with two U.S. officials that a suicide bomber was responsible for the attack. The suspect traveled by subway to Victoria Station and detonated the explosive device near the ticket area as the concert was ending and people were exiting the venue, it added. Parts of the suspected suicide bomber's body have been recovered, CBS News added.

ADVERTISEMENT British Prime Minister Theresa May will temporarily suspend her reelection campaign ahead of the June 8 contest in the wake of the attack and expressed condolences for the killed and injured. She confirmed that the incident "is being treated by the police as an appalling terrorist attack." Almost 60 people were injured. Hopkins said they were being treated at six different hospitals across Greater Manchester. "My thoughts are very much with those who have been injured and lost their lives and loved ones at this terrible time," Hopkins said. "We’re doing all that we can to support them." "We are currently treating this as a terrorist incident until we know otherwise. We are working closely with the national counter terrorism policing network and UK intelligence partners."

He urged people to "avoid the area around Manchester Arena so that emergency services can continue to effectively deal with the incident at that location." The Department of Homeland Security released a statement late Monday indicating it was in touch with authorities in the U.K. following the incident. JUST IN: DHS on #ManchesterArena incident: “No information to indicate a specific credible threat involving music venues" in the U.S. pic.twitter.com/YKUGhyB2GQ — ABC News (@ABC) May 23, 2017 There is "no information to indicate a specific credible threat involving music venues in the United States," the statement said. "However, the public may experience increased security in and around public places and events as officials take additional precautions." Homeland Security said it was "working with our foreign counterparts to obtain additional information about the cause of the reported explosion as well as the extent of injuries and fatalities. "

CNN also reported that authorities believe they have identified a possible suicide bomber on the scene.

Latest: Male at scene of #ManchesterArena attack identified as probable suicide bomber, @evanperez & @PamelaBrownCNN reporting — Jim Sciutto (@jimsciutto) May 23, 2017 Police carried out "a precautionary controlled explosion in Cathedral Garden" after the incident and confirmed that it had disposed of "abandoned clothing, not a suspicious item." The U.S Embassy in London also issued a statement about the explosion, urging people to "heed guidance from local authorities and maintain security awareness." The BBC on Monday reported that witnesses heard a “huge bang” following the concert.

“A bang went off and everyone stopped and screamed. ... We basically hit the deck,” Josh Elliot told BBC Radio 5 Live. “It was bedlam ... it was horrific.”

“We got up when we thought it was safe and got out as quickly as possible. We just got out as quickly as possible because we didn’t know what was going on.”

Representatives for Grande on Monday confirmed to ABC News that the pop singer was not harmed.

ABC reported that Manchester Victoria station was evacuated following the event, with trains there unable to run.

Reuters on Monday reported that Britain is on its second highest alert level of “severe,” meaning an attack by militants is considered highly likely.

Manchester Arena is the largest indoor arena in Europe, according to its website, and can hold 21,000 people.

Updated on May 23 at 6:12 a.m.