British Home Secretary Amber Rudd said Manchester Arena bomber Salman Abedi "likely" had accomplices and she criticized the USA government for leaking information about his identity.
Britain raised its threat level from terrorism to "critical" after an emergency government meeting late Tuesday amid concerns that the 22-year-old Abedi may have accomplices who are planning another attack.
One of the forces that supports the GNA posted a picture on its Facebook page of Hashem Abedi after detaining him.
Meanwhile, it was reported that the bomber's younger brother, Hashem Abedi, had also been detained in Tripoli on suspicion of links with Islamic State.
Four people have been arrested in connection with the bombing.
The name was being withheld for operational security and was released as raids were underway both in Manchester and in Libya where the bomber's father lives.
In London, Changing the Guard at the Palace was cancelled and Parliament was closed to the public, with soldiers also likely to be on duty his weekend's FA Cup final at Wembley and the Twickenham rugby premiership final. He fled Libya in 1993 when the forces of Muammar el-Qaddafi issued a warrant for his arrest and received political asylum in Britain, where Salman Abedi was born and raised. The youngest victim was 8-year-old Saffie Roussos.
Police also raided and searched a property elsewhere in Manchester where Abedi's brother Ismail is thought to have lived. Lisa Lees Lauren Ashleigh Lees said that her mother, 43-year-old Lisa Lees, was among the victims.More news: Man U rediscovers aura, winning mentality under Mourinho
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The elder Abedi told The Associated Press by telephone from Tripoli: "We don't believe in killing innocents". Several details, including the identity of the attacker, appeared on United States media outlets before British security forces were ready to release the information.
Former Libyan security official Abdel-Basit Haroun told the AP that the elder Abedi was a member of the Libyan Islamic Fighting group in the 1990s, which had links to al-Qaida. Insurance contracts already contain specific terrorism clauses, but there are reports of a surge in demand by event organizers wanting to review their coverage in the wake of Monday's bombing in Manchester.
"He stood up and started calling the imam - 'You are talking bollocks, '" Ramadan said.
"The concern is that there may be others out there who helped him to make the bomb".
As the UK's terror alert remained at its maximum "critical" level, it was also revealed Thursday that British intelligence foiled five planned terror operations since an attack at Westminster on March 22.
She also complained about USA officials leaking sensitive information about Abedi to the press, saying that could take "the element of surprise" away from Britain's security services and police.
A Polish couple who had come to collect their daughters from the concert in Manchester are among the dead, Poland's foreign minister said Wednesday. As of Wednesday morning, police say, they have identified all of the fatalities and contacted all of the families involved.
Asked if officers are looking for the person who made the bomb, he said: "I think it's very clear that this is a network that we are investigating and as I've said, it continues at pace, this extensive investigation is going on and activity taking place across Greater Manchester as we speak".