Police said 22 people were killed and approximately 59 others were injured in an explosion at Manchester Arena in the U.K. on Monday night

Ariana Grande has spoken out about the devastating news of 22 people killed and at least 50 others injured in an explosion at her Manchester Arena concert in the U.K. on Monday night.

“Broken. From the bottom of my heart, I am so so sorry. I don’t have words,” Grande tweeted following police confirmation of the number of deaths and injuries. During the show, a concertgoer captured footage of the star’s fans singing along to her hit song “One Last Time.”

Chief Constable Ian Hopkins said the explosion occurred around 10:33 p.m. local time near the ticket office outside the arena following Grande’s Dangerous Woman show.

2016 American Music Awards - Arrivals
Credit: Frederick M. Brown/Getty

Chief Constable Ian Hopkins said the explosion occurred around 10:33 p.m. local time near the ticket office outside the arena. The attack was carried out by a lone suspect carrying a bomb, Hopkins said.

“The attacker, I can confirm, died at the arena. We believe the attacker was carrying an improvised explosive device, which he detonated, causing this atrocity,” Hopkins said.

He added, “We have been treating this as a terrorist incident and we believe, at this stage, 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.”

The victims’ identities were not confirmed by authorities, though numerous reports highlighted Grande’s largely youth-skewing fan base, including children, teens and young adults.

Credit: Joel Goodman/LNP/REX/Shutterstock
Credit: Joel Goodman/LNP/REX/Shutterstock

“Ariana is okay,” her rep said in a statement to PEOPLE. “We are further investigating what happened.”

British Prime Minister Teresa May says her thoughts are with victims and families after what is being treated by police “as an appalling terrorist attack.”

Many from the music world and Hollywood celebrities expressed their condolences as well.

Credit: Dave Thompson/Getty

“It was the scariest thing I’ve ever seen in my life,” concertgoer Esme Findlay, 20, told PEOPLE. “It was really loud; it sounded like a huge bang.”

Attendee Lori Templeton, 15, shared with PEOPLE: “It was so so loud. Everyone turned and looked, and people started screaming and running out exits and back into the arena. People were screaming and running and falling over chairs. It was really scary. … For the first time in my life, I thought I was going to die. “