Manchester bombing probe police hunt for suitcase carried by Salman Abedi

Fourteen people are now in custody in relation to the attack, including a 23-year-old man arrested early Monday in the southern coastal town of Shoreham-by-Sea on suspicion of terrorism offenses.

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.

So far, 16 people have been arrested in connection with the investigation, with 14 men remaining in custody for questioning, and two people having been released without charge.

MI5 is to hold an inquiry into the way it dealt with warnings from the public that the Manchester suicide bomber, Salman Abedi, was a potential threat.

He said the police believe Abedi was in possession of this case in the days before the attack.

Earlier the BBC reported that the MI5 had been alerted about Abedi's extremist views at least three times before he brought a home-made bomb to the exit of Manchester Arena last week. As runners pounded the streets of the northwestern English city, police arrested a 25-year-old man in the eastern Old Trafford area, bringing the number now detained on United Kingdom soil in connection with the attack to 12.

When asked how many potential militants the government was anxious about, Rudd said the security services were looking at 500 different potential plots, involving 3,000 people as a "top list", with a further 20,000 beneath that.

Police investigating the suicide attack in Manchester are searching a landfill site on the outskirts of Bury.

Britain has downgraded its security level from its highest level, but it still remains at "severe", meaning an attack is highly likely. Abedi's elder brother Ismail is among the suspects being held in Britain, and a younger brother and Abedi's father have been detained in Libya.

British officials have confirmed he had recently returned from Libya and the officers said that police needed information about his movements since his return to Britain on May 18.

The home secretary would not comment specifically on what the security service knew about Abedi, but insisted it was right for MI5 to review its processes because "the threat is always changing".

"Until the operation is complete, we can't be entirely sure that it is closed", she said.

Early morning raids were carried out at a house in Manchester, along with searches carried out in Chester and Shoreham-by-Sea, on the south coast of England.

  • Leroy Wright