Almost 23000 terror suspects at large in the country, believe United Kingdom spies

They added that additional officers, including armed officers, will be on patrol especially at a number of events on the weekend to ensure the security and safety of everyone.They also made an appeal to the public for information about the bomber's movements since 18 May, when he returned to the United Kingdom from Libya.

A Greater Manchester police statement said, "We have made significant progress in this fast moving and complex investigation, working with the national counter terrorism policing network and United Kingdom intelligence partners and securing the arrests of 11 people who remain in custody".

"We should be clear about what this means: A threat level of severe means an attack is highly likely, the country should remain vigilant", she said.

On May 26, Grande broke her silence following the May 22 attack on her concert at the Manchester Arena and released a statement on Twitter, promising to return to the English city to host and perform at a benefit concert to raise funds for the victims.

Investigators say they have a 1,000-strong team working "around the clock" on the probe and have significant details on Abedi's associates and movements, his finances, and how the explosive was built.

Two unarmed police officers remained on guard outside the entrance to Granby House, believed to contain the flat in question, according to an AFP correspondent at the scene.

On Sunday, a 25-year-old man was arrested in Manchester on suspicion of terror offenses in the Old Trafford area. All are men between the ages of 18 and 44.

Police issued CCTV stills of Salman Abedi, bespectacled and casually clothed, in a plea for information about his movements between May 18 and the attack. His father said Abedi was in Libya until earlier this month and had told family that he planned to go to Saudi Arabia on a pilgrimage, police said.

Officers investigating the Manchester Arena attack are also searching an address in Moss Side, the force said.

"There will be more arrests and there will be more searches", he said. Photos showed an army bomb-disposal unit at the property.

"We thought he must have been a drug dealer or doing witchcraft", El-Hudarey told the BBC.

Rudd said Sunday that intelligence agencies were monitoring 3,000 suspected extremists and had a wider pool of 20,000 people of interest.

A total of 116 people required hospital care, police said.

Armed police mingled with spectators as crowds gathered to watch the runners, including mayor of Greater Manchester Andy Burnham.

Armed police were on the streets Saturday outside London's Wembley Stadium, and security guards conducted extra bag checks, as 90,000 fans arrived for the FA Cup soccer final between Chelsea and Arsenal, one of the biggest sporting events of the year.

Additional reporting the Press Association.