Queen Elizabeth II called Monday’s suspected suicide attack at an Ariana Grande concert in Manchester, England, an “act of barbarity.”

“The whole nation has been shocked by the death and injury in Manchester last night of so many people, adults and children, who had just been enjoying a concert,” she said in a statement on Tuesday. “I know I speak for everyone in expressing my deepest sympathy to all who have been affected by this dreadful event and especially to the families and friends of those who have died or were injured.”

The blast, which killed at least 23 people including the attacker and injured 59, occurred outside Manchester Arena near the venue’s box office just moments after Grande concluded her performance. Concert attendees, many of them Grande’s young fans and their parents, were sent into panic.

British police said they are treating the blast as a terrorist incident. While the identities of all the victims have not yet been released, many of those affected are believed to be children.

Grande, who was set to perform in London next, suspended her tour indefinitely.

broken.

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