Pop star Ariana Grande said on Monday she was "broken" five hours after a bombing killed 19 people and wounded dozens of others at her concert in Manchester, England.

Making her first comment since an explosion detonated just outside Manchester Arena at the end of her performance there, Grande said on Twitter: "broken. from the bottom of my heart, I am so so sorry. I don't have words."

Representatives for Grande have said that the 23-year-old pop star was physically "okay" following the blast, which British authorities say was being treated as a terrorist attack.

Two U.S. officials have told Reuters on condition of anonymity that initial signs pointed to a suicide bomber as being responsible for the bombing.

Grande was performing in Manchester during the European leg of a concert tour to support her latest album, "Dangerous Woman."

She was scheduled to perform at London's O2 arena on Thursday and then in Belgium, Poland, and Germany in the coming weeks. It was not immediately clear whether those concerts would go forward following Monday's attack.

Grande, who starred in the Broadway musical "13" and on the Nickelodeon TV series Victorious before releasing her solo debut album, is credited with having an exceptionally broad vocal range for a pop star.

She is best known for her singles "Problem," and "Break Free" from her sophomore album, My Everything.