MI5 is to hold an inquiry into how it dealt with public warnings that the Manchester suicide bomber Salman Abedi posed a potential threat.

Britain's MI5 is to hold an inquiry into how it dealt with public warnings that the Manchester suicide bomber Salman Abedi posed a potential threat, the BBC reported on Monday.

MI5 was alerted to Abedi's extremist views at least three times, the BBC said.

It is highly unusual for British authorities to make public that the security service is conducting an internal investigation into possible lapses.

Interior Minister Amber Rudd told Sky News that this was a "right first step” for MI5 to take in the wake of the bombing that killed 22 people at a pop concert by U.S. singer Ariana Grande.

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.

A source had told Reuters last week that Abedi was one of “a larger pool of former subjects of interest” whose risk remained subject to review by MI5.

Police on Monday arrested a 16th person in connection with the Manchester suicide bombing, the deadliest attack in Britain for 12 years.

At least 22 people, including children — one as young as eight-years-old — were killed and 59 injured in a “callous” suicide attack in the northern English city of Manchester on Monday night. One person has been arrested in connection with the attack.

As early as Tuesday morning Manchester police said they knew the identity of the attacker, but declined to name him publicly. A U.S. official, however, told Associated Press that the suicide bomber was Salman Abedi.

The attack came exactly two months after a 52-year-old British citizen drove a car into pedestrians at Westminster and fatally stabbed an unarmed police officer.

The bombing at the close of a pop concert at the popular Manchester Arena is the country’s deadliest terror attack since 2005, when 52 people were killed and several hundreds injured in a series of bomb blasts in central London.

The Islamic State has claimed responsibility for the Manchester attack via social media, against what it described as “crusaders”. It described the attacker as a “soldier of the caliphate.”