British intelligence re-examines suicide bomber's file after Manchester attack

Britain's intelligence agency, MI5, has begun an internal review of how it handled intelligence on Manchester suicide bomber Salman Abedi, who was known to the authorities but not under active investigation, a source told Reuters on Monday.

Interior Minister Amber Rudd said the review was the "right first step" for the intelligence agency to take in the wake of the May 22 bombing that left 22 people dead after a concert by American singer Ariana Grande.

MI5 is subject to scrutiny by a committee of Parliament, and it is highly unusual for British authorities to make public that the security service is conducting its own internal investigation into possible lapses.

"The review will look at what was known about Abedi, what decisions were made about the intelligence and what, if anything, could have been done differently," the source said, speaking on condition of anonymity.

"This is a review that would seek to answer whether there are lessons to be learned from how the Security Service handled the intelligence on Abedi."

The source told Reuters that Abedi was not among the 3,000 people currently under active investigation by MI5, although he was one of about 20,000 people known to the agency, which focuses on countering terrorism and espionage.

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The BBC said MI5 was alerted at least three times to the 'extremist views' of Abedi, a 22-year-old who grew up in Manchester in a family of immigrants from Libya. It was not possible to confirm that report.

"This is an ongoing investigation so I'm not going to be drawn into comments on the actual man who committed this crime," Rudd told BBC television, declining to say what was known about Abedi and when.

Arrest in southeast England

Also on Monday, British police arrested a 23-year-old man on the south coast of England, hundreds of kilometres south of Manchester.

Greater Manchester Police said the man was arrested in Shoreham-by-Sea on suspicion of terrorism offences, and an address there was searched.

The arrest is the 16th since the attack, with 14 currently in custody.

All are being held on suspicion of violating the Terrorism Act.

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Officers also released a close circuit television image of Abedi holding a blue suitcase on the day of the attack and asked members of the public to come forward with information as they focused on his movements between May 18 and May 22.

"We have no reason to believe the case and its contents contain anything dangerous, but would ask people to be cautious," Detective Chief Superintendent Russ Jackson from the North West Counter Terrorism Unit said in a statement.

Police and security services have said very little about the network believed to be behind Abedi. His elder brother Ismail is among the suspects being held in Britain, and a younger brother and Abedi's father have been detained in Libya.

Authorities say Abedi returned to Britain from Libya on May 18, and likely completed assembling his bomb at a rented apartment in central Manchester.

Britain's official terror threat level was set at critical in the days after the attack, but was downgraded Saturday to severe. The country remains on high alert, however, as officials caution that some suspects who helped Abedi may still be at large.

The alert is front and centre as Britons go to the polls on June 8 to elect a new government.