LONDON (Reuters) - Britain's threat level will remain at its highest level while police hunt down the suspected network of a suicide bomber who killed 22 people at a concert in Manchester, interior minister Amber Rudd said on Friday.
The Manchester bombing was the deadliest attack in Britain since July 2005, when four British Muslim suicide bombers killed 52 people in coordinated attacks on London's transport network.
Top intelligence and security officials in Britain's Joint Terrorism Analysis Centre (JTAC) on Tuesday raised the threat level to "critical" - meaning an attack is expected imminently - the day after the Manchester attack.
"JTAC have assessed that the level of threat should remain at critical while the operation continues," Rudd told Sky News.
Manchester Police are currently holding eight men in custody and further searches were continuing on Friday as officers sought to determine if the bomber, 22-year-old Salman Abedi, was supported by a wider network.
Britain has only had a threat level of "critical" twice before, and it was last at this level in June 2007 after a failed attempt to bomb Glasgow airport.
The heightened level of security has seen the army assist the police in guarding high profile sights, and also prompted authorities to put armed police on British trains for the first time ever.
Security is especially tight ahead of the weekend. Monday is a public holiday in Britain, and the weekend sees a number of high-profile events such as the soccer FA Cup final in London on Saturday.
However security minister Ben Wallace said that a memo sent to hospital staff telling trauma wards to be ready ahead of the bank holiday weekend was part of a general heightened sense of preparedness and not a response to specific intelligence.
"That is predominantly precautionary... There is no specific threat against an individual event," Wallace said on BBC radio.
Police made further searches on Friday at addresses in south Manchester and St Helens, 20 miles west of Manchester.
The 8 men in custody are all aged between 18 and 38, Greater Manchester police said. A total of 10 arrests have been made, but a 16-year-old boy and a 34-year-old woman have been released without charge, police said.
Reporting by Alistair Smout; editing by Michael Holden