Several hours after an explosion characterized as a “terrorist incident” killed 22 people after her concert tour stop at Manchester Arena in England, pop star Ariana Grande said she is “broken” in the wake of the horrific tragedy.

“from the bottom of my heart, i am so so sorry,” the 23-year-old singer tweeted late Monday night. “i don’t have words.”

About 50 other concertgoers were injured in the attack, according to Manchester police. U.S. security officials told The Washington Post that evidence suggested a suicide bombing. The explosion occurred outside the venue, just as Grande finished the show and people started to leave the arena.

Grande’s manager, Scooter Braun, also released a statement on Twitter: “Words cannot express our sorrow for the victims and families harmed in this senseless attack. We mourn the lives of children and loved ones taken by this cowardly act. We are thankful for the selfless service tonight of Manchester’s first responders who rushed toward danger to help save lives. We ask all of you to hold the victims, their families, and all those affected in your hearts and prayers.”

Grande has a fiercely loyal following of young fans ever since her days on Nickelodeon comedies “Victorious” and “Sam & Cat.” Over the last few years, she’s become one of the most famous pop stars in the world and a four-time Grammy nominee.

Late Monday, TMZ reported that Grande has suspended the rest of her “Dangerous Woman” tour, which was next scheduled for a stop in London on Thursday.

Rapper BIA, Grande’s opening act on her tour, also tweeted after the show:

Throughout Monday night, tributes and condolences poured in from stars across the world: