MANCHESTER, England (AP) -- British police investigating the Manchester Arena bombing made a new arrest Friday while continuing to search addresses associated with the attacker who killed 22 people.
Seven other men are in custody in connection with Monday's blast, all are being held on suspicion of offenses violating the Terrorism Act. Their ages ranged from 18 to 38.
A 16-year-old boy who had been arrested was released without charge, police said.
Britain's security level has been upgraded to "critical" meaning officials believe another attack may be imminent.
Authorities are chasing possible links between the bomber, Salman Abedi, and militants in Manchester, elsewhere in Europe, and in North Africa and the Middle East.
Abedi, a college dropout who had grown up in the Manchester area, was known to security services because of his radical views. He was the son of Libyan parents who migrated to Britain in the early 1990s.
He reportedly was in contact with family members just before the attack.
The name of the man arrested in the early hours Friday and those of the seven others in custody were not released. No one has yet been charged in the bombing.
London police say extra security is being added for major sporting events this weekend including the FA Cup Final at Wembley Stadium.
Chief Superintendent Jon Williams said Friday extra protection measures and extra officers are being deployed throughout the capital because of the increased terrorist threat level.
He said fans coming to football and rugby matches this weekend should come earlier than usual because of added security screening.
Williams said "covert and discrete tactics" will also be in place to protect the transport network.
He says police want the approach to be "unpredictable" and to make London "as hostile an environment as possible to terrorists."
British police working on the case have resumed intelligence-sharing with U.S. counterparts after a brief halt because of anger over leaks to U.S. media thought by Britain to be coming from U.S. officials.
British officials say that have receive assurances from U.S. authorities that confidential material will be protected.
Campaigning in Britain's general election, set for June 8, is resuming after being suspended because of the bombing late Monday following an Ariana Grande concert.
Labour leader Jeremy Corbyn plans to use a speech Friday to link Britain's actions overseas to the increased extremist threat at home.