LONDON (AP) — More than 250 survivors of the bombing that killed 22 people at a 2017 Ariana Grande concert in Manchester, England, are taking legal action against Britain’s domestic intelligence agency, lawyers said.

Lawyers from three law firms said Sunday they have submitted a group claim on behalf of more than 250 clients to the U.K.'s investigatory powers tribunal. They said they could not provide further details because it was an ongoing legal matter.

Suicide bomber Salman Abedi set up a knapsack bomb in Manchester Arena at the end of Grande’s concert on May 22, 2017, as thousands of young fans were leaving. More than 100 people were injured, many of them children and teenagers. Abedi died in the explosion.

An official inquiry reported last year that Britain’s domestic intelligence agency, MI5, didn’t act swiftly enough on key information and missed a significant opportunity to prevent the bombing, the deadliest extremist attack in the U.K. in recent years.