Britain's domestic counterintelligence and security agency, MI5, is to hold an inquiry into how it dealt with public warnings that Manchester suicide bomber Salman Abedi posed a potential threat, the BBC reports.
MI5 was alerted to Abedi's extremist views at least three times before the May 22 attack in Manchester that killed 22 people, including seven children, at a concert by U.S. singer Ariana Grande.
Home Secretary Amber Rudd told BBC television on May 29 that it was right for MI5 to review its processes.
It is highly unusual for British authorities to make public that the security service is conducting an internal investigation into possible lapses.
The security service will examine assumptions that were made about Abedi before the attack, and has launched a "post-incident investigation" into how the bomber was overlooked, the BBC said.
A separate report is also being prepared for ministers and those who oversee the work of the service, it added.
Abedi was one of "a larger pool of former subjects of interest" whose risk remained subject to review by MI5, the Reuters news agency reported last week, citing an unnamed source.
Also on May 29, police arrested a 16th person in connection with the Manchester suicide bombing, the deadliest attack in Britain for 12 years.
The 23-year-old man was arrested in the southern English town of Shoreham-by-Sea "on suspicion on offences contrary to the terrorism act," Greater Manchester Police said on Twitter.
A total of 16 people have been arrested in connection with the attack.
Two were released without charge, while 14 men remained in custody for questioning, the police said.