Manchester bomber Salman Abedi 'known up to a point to intelligence services'
Manchester bomber Salman Abedi was known to the intelligence services "up to a point", Home Secretary Amber Rudd has said.
The Government raised the terrorism threat level to "critical" - the highest possible rating - on Tuesday amid fears another attack is imminent.
Ms Rudd disclosed that the intelligence services had been aware of British-born Abedi, who is reported to have recently returned to the UK from a visit to Libya.
She told Sky News: "We do know that he was known up to a point to the intelligence services".
Ms Rudd refused to be drawn about the nature of the information held by the intelligence services about Abedi.
"I am sure that we will get more information about him over the next few days and the next few weeks," she said.
She said the threat level would remain at a heightened state while the investigation into the attack continued.
"It is an ongoing operation which means that the investigation is continuing to find leads," she said.
"So until we can be reassured that there is no continued activity around this operation, that is entirely safe around this operation, then it is right that we are at this heightened state of alert.
"It is operationally driven, it is intelligence-driven and we must make sure that we allow our counter-terrorist police, our police and our intelligence services to get on and do their job and this helps give them the space to do just that."
Announcing the raising of the threat level late on Tuesday, Prime Minister Theresa May said a "wider group of individuals" could have been involved in the Manchester Arena blast.
In a sign of the increased threat, the military could be deployed to support armed police officers, Mrs May added during a live televised statement from Downing Street.
Monday night's attack at a concert by US pop star Ariana Grande left 22 people dead, including an eight-year-old girl, and dozens injured.
As counter-terrorism agencies mounted a massive inquiry into the outrage, the worst terrorist attack since 52 innocent people were killed in the July 7 bombings in London in 2005:
:: Police have arrested a 23-year-old man near a Morrisons in Chorlton, south Manchester, in connection with the inquiry
:: Mrs May vowed that the "spirit of Manchester and the spirit of Britain is far mightier than the sick plots of depraved terrorists"
:: Among the first victims to be named were eight-year-old Saffie Roussos from Leyland and teenagers Olivia Campbell, 15, from Bury and Georgina Callander from Chorley.
:: Many of the 59 people hurt in the attack were treated for life-threatening injuries. Twelve of those rushed to hospital were children
The Islamic State terror group claimed responsibility for the barbaric attack, which involved a home-made device packed with nuts and bolts which exploded in the venue's foyer as thousands of young people were leaving.
Abedi, 22, is believed to have been born in Manchester and of Libyan descent. He studied business at Salford University but dropped out before completing his degree.
He is thought to have attended the Manchester Islamic Centre, also known as Didsbury Mosque, along with his parents and siblings.
A family friend, who asked not to be named, described him as "normal" and said they were known to the Libyan community in the city.
He told the Press Association: "He was always friendly, nothing to suggest (he was violent). He was normal, to be honest."
Abedi was named after armed officers carried out a raid and controlled explosion at an address in south Manchester where he was registered as living.
Elsewhere in the city, the first arrest was made in connection with the inquiry when a 23-year-old man was detained near a Morrisons in Chorlton.
The terror threat level was increased after investigations revealed he may not have acted alone.
Mrs May said Operation Temperer, allowing military personnel to take to the streets, is now in force.
She will chair a meeting of the Government's emergency Cobra committee at 9.30am on Wednesday.
Meanwhile, fears were growing for Chloe Rutherford, 17, and Liam Curry, 19, a couple from South Shields, Eilidh MacLeod, from Barra in Scotland, Martyn Hett and Wendy Fawell.
All were believed to have been at the concert and have not been traced since the attack.
The death of Saffie, the youngest known victim of the attack, was described by her headteacher as "heartbreaking".
Chris Upton, of Tarleton Community Primary School, said: "Saffie was simply a beautiful little girl in every aspect of the word."
On Tuesday Charlotte Campbell launched a desperate bid to find her daughter and made several emotional appeals on television.
She later said on Facebook: "RIP my darling precious gorgeous girl Olivia Campbell taken far far to soon go sing with the angels and keep smiling mummy loves you so much."
Another victim was named by her college as Ms Callander, who was studying health and social care at Runshaw College in Leyland, Lancashire.
Kelly Brewster, from Sheffield was reported missing by relatives who appealed for help finding her.
Her partner, Ian Winslow, later said on Facebook: "Kelly Brewster wasn't one of the unidentified hospital patients. She has sadly passed away in the terror attack yesterday.
"Kelly really was the happiest she has ever been and we had so many things planned together. My daughter Phoebe will be absolutely devastated like we all are."
Tributes were also paid to 26-year-old John Atkinson from Bury, who was named by friends on Facebook as an apparent victim.
The country's senior anti-terror police officer said there were "gaps in our knowledge" about Abedi which had led to the increased threat level.
Metropolitan Police Assistant Commissioner Mark Rowley said: "We are moving at pace, we are making arrests, we are doing searches but, not unsurprisingly, there are still gaps in our knowledge.
"Whilst we are chasing those gaps down, on a precautionary basis, based on that judgment, JTAC (the Joint Terrorism Analysis Centre) have made this judgment about the threat level and we will respond in our policing stance to that decision."
Greater Manchester Police Deputy Chief Constable Ian Pilling said the raised level will support the "significant" resources the force has in place.
He also praised the "tremendous strength and resilience" shown in Manchester on Tuesday, adding: "We need this to continue in the difficult days ahead."