People gesture as they attend a vigil in Trafalgar Square, London Tuesday May 23, 2017 for the victims of the attack which killed over 20 people as fans left a pop concert by Ariana Grande in Manchester on Monday night. She said Abedi had been known to security services before the bombing. Officials are examining Abedi's trips to Libya as they work to piece together his allegiances and foil any new potential threats.
Three men have been arrested as part of the Manchester bomb investigation, United Kingdom police say.
The suicide bomber who murdered 22 people and injured 59 at Manchester Arena has been named by police as Salman Abedi, a 22-year-old British-born man whose parents had fled the Gaddafi regime in Libya. In London, public tours of the parliament complex and the changing of guard ceremony in Buckingham Palace have been cancelled.
According to Rudd, up to 3,800 troops will be deployed on the streets around Britain.
Armed police officers stand on duty outside St Paul's Cathedral in London, Britain, May 24, 2017. Ramadan Abedi told the AP that when he spoke to his son Abedi five days ago, he sounded "normal".
The elder Abedi told the Associated Press by telephone from Tripoli: "We don't believe in killing innocents.
He said his other son, Ismail, was arrested in England on Tuesday morning.
Deputy Chief Constable Ian Pilling said the announcement of raising the threat level to its highest will provide the force with additional resources to conduct their investigations.
Monday's attack came just over two weeks before Britain votes in a general election and campaigning was suspended by all the main political parties.
British Prime Minister Theresa May chaired a meeting Wednesday of her emergency security cabinet group to talk about intelligence reports on Abedi and concerns that he might have had outside support.
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Amber Rudd, the Home Secretary, confirmed Abedi had recently returned from Libya before launching the bomb.
His 22 victims included an eight-year-old girl, several teenage girls, a 28-year-old man and a Polish couple who had come to collect their daughters.
ISIS, now being driven from territories in Syria and Iraq by Western-backed armed forces, claimed responsibility for the Manchester attack, but there appeared to be contradictions in its account of the operation.
French Interior Minister Gerard Collomb said British investigators had told French authorities Abedi had probably travelled to Syria as well. He did not elaborate but said it's unclear whether Abedi was part of a larger network of attackers.
Monday's terror attack has raised the terror threat to be raised to critical - the highest level - which means an attack is "expected imminently".
She also complained about US officials leaking sensitive information about Abedi to the USA media.
Pressed on whether the Americans had compromised the investigation, she said: "I wouldn't got that far, but I can say they are perfectly clear about the situation and that it shouldn't happen again".
"Thanks to everyone who has been in touch", the O2 said on Twitter. They are both now in separate hospitals being treated for injuries, friends said.
Military personnel and police have been deployed to protect key sites including Buckingham Palace, Downing Street, the Palace of Westminster and embassies. London Police Commander Jane Connors said the goal was to "make our city as hostile an environment as possible for terrorists to plan and operate".