Images published by The New York Times showed that the bomb intended to inflict maximum damage
The younger brother and father of the suicide bomber who killed 22 people at a concert venue in Manchester were arrested in Tripoli on suspicion of links with the Islamic State (IS) group, a spokesman for a local counter-terrorism force said on Wednesday.
The force, known as Rada, detained Hashem Abedi, who was born in 1997, and his father Ramadan Abedi, on Tuesday evening, spokesman Ahmed Bin Salem told Reuters.
Hashem Abedi had been in touch with attacker Salman Abedi, Bin Salem said.
"We have evidence that he is involved in Daesh (Islamic State) with his brother. We have been following him for more than one month and a half," Bin Salem said.
"He was in contact with his brother and he knew about the attack."
The counter-terrorism force detained Ramadan Abedi outside his home in the Tripoli suburb of Ayn Zara. A witness said he was handcuffed by armed men who drove him away in two unmarked vehicles.
Salman Abedi, the bomber, 22, was born in Britain to Libyan parents. Britain's home secretary, Amber Rudd, said earlier that he had recently returned from Libya and had likely not acted alone.
British police on Wednesday said they were investigating a "network" in their probe of the attack.
"I think it's very clear that this is a network that we are investigating," said Ian Hopkins, the chief constable of Greater Manchester Police.
"And as I've said, it continues at a pace. There's extensive investigations going on and activity taking place across Greater Manchester as we speak."
Hopkins' comments follow a similar admission earlier in the day by Rudd.
"It seems likely, possible, that he wasn't doing this on his own so the intelligence services and the police are pursuing their leads in order to make sure they get all the information ... that they need to keep us safe," Rudd told BBC radio.
Asked to confirm whether Abedi had recently come back from the country, Rudd told the BBC: "Yes, I believe that has been confirmed. When this operation is over, we will want to look at his background and what happened, how he became radicalised and what support he might have been given."
Police on Wednesday made four more arrests in south Manchester and one in Wigan over the attack. Later in the evening a woman and a man were also detained, bringing the total number of suspects to seven.
"We have made an arrest in Wigan this afternoon in connection with the investigation into the horrific incident at Manchester Arena," police said in a statement about the fifth arrest.
"When arrested, the man was carrying a package which we are currently assessing."
Terror level increased
Soldiers were deployed to central areas of London, hours after the government raised the terrorism threat level to its highest - meaning another attack could be "imminent".
On Tuesday, the Islamic State group claimed the attack, which targeted people who were attending the concert of US singer Ariana Grande.
Rudd said she was not surprised that IS has claimed the attack, but that she could not confirm any link.
“We don't have that information yet,” she said.
Details about Abedi, including his name, were revealed by unidentified US officials. Rudd criticised such leaks.
"The British police have been very clear that they want to control the flow of information in order to protect operational integrity, the element of surprise, so it is irritating if it gets released from other sources and I have been very clear with our friends that should not happen again," she said.
Asked whether the US leaks had compromised the investigation, Rudd said: "I wouldn't go that far but I can say that they are perfectly clear about the situation and that it shouldn't happen again."
She also said that more money would be given to the controversial Prevent counter-terrorism programme, should the Conservatives be re-elected at the general election on 8 June.
Andy Burnham, the Labour Mayor for Greater Manchester, said on Wednesday that he had concerns about the Prevent programme and that it was important not to raise suspicion of an entire community.
Cautioning against describing the attack as “Islamic terror,” Burnham said that: “We have to be careful of the language used … I think sometimes the language used does not help us and further increases this sense of distrust.”
“[Abedi] no more in my view represents the Muslim community than the person who killed my friend, Jo Cox, represents all white British men,” he told the BBC, referring to the killing last year of a Labour politician by a white man with links to far-right groups.
British Prime Minister Theresa May received condolence calls from several foreign leaders on Wednesday, her spokesman said.
May took calls from German Chancellor Angela Merkel, King Salman of Saudi Arabia, Swedish Prime Minister Stefan Lofven, and Indian Prime Minister Narendra Modi, he said.
"King Salman of Saudi Arabia called to offer his condolences and said Saudi Arabia strongly denounces and condemns this brutal terrorist attack which defies all international humanitarian norms," the spokesman said in a statement.
"They agreed the UK and Saudi Arabia would continue working closely together to counter terrorism and violent extremism."
On Tuesday, May spoke to US President Donald Trump, French President Emmanuel Macron, Italian Prime Minister Paolo Gentiloni and Australian Prime Minister Malcolm Turnbull.
Vigil in central Manchester, 23 May (Reuters)
Photos show maximum damage
The bomb used in the attack packed a powerful charge together with a shrapnel of nuts and screws meticulously arranged for maximum damage, according to photographs published by the New York Times.
The Times published eight exclusive pictures, which were unsourced but appeared to be police photographs taken at Manchester Arena.
Initial analysis of the various elements photographed at the scene suggests that the suicide bomber carried "an improvised device made with forethought and care," concealed most likely within a backpack but also possibly in a vest, wrote the paper.
The images notably suggest the suicide bomber - or a possible team helping him - had a remote detonator setup, to back up a hand-held detonator found at the scene.
The newspaper said there were no initial details of the type and strength of the explosive used in the attack.
But, combined with the location of the bodies of those struck by the bomb, and the remains of the bomber himself, the Times said, "All of these are indicators of a powerful, high-velocity charge, and of a bomb in which its shrapnel was carefully and evenly packed."
"Such redundancy could give the bomber or a cell more than one option for deploying the device, and further suggests that the bomb was not as simple in design as many terrorist devices, which often are crude and prone to failure or haphazard effect," the Times said.
The BBC reported that security services thought the bomb was too sophisticated for Abedi to have built by himself.
The photos published by the Times raised further concerns about leaks from the US.
"We greatly value the important relationships we have with our trusted intelligence, law enforcement and security partners around the world," a spokesman for the National Police Chiefs council said on Wednesday after the pictures were published.
"When that trust is breached it undermines these relationships, and undermines our investigations and the confidence of victims, witnesses and their families. This damage is even greater when it involves unauthorised disclosure of potential evidence in the middle of a major counter terrorism investigation."
Meanwhile, Grande's representative said on Wednesday she was suspending her tour to assess the situation and to "pay our proper respects to those lost". The US singer had been scheduled to perform two shows at London's O2 arena this week.