The Manchester suicide bomber who killed 22 people at a concert venue packed with children had recently returned from Libya, a British minister said, and her French counterpart said he had links with Islamic State and had probably visited Syria too.
Interior minister Amber Rudd said Salman Abedi had likely not acted alone, and troops were being deployed to key sites across Britain to help prevent further attacks after the official threat level was raised to "critical".
Police made three new arrests in South Manchester on Wednesday in connection with the concert bombing. They provided no details on the individuals held.
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Rudd said up to 3,800 soldiers could be deployed on Britain's streets, taking on guard duties at places like Buckingham Palace and Downing Street to free up police to focus on patrols and investigation. An initial deployment of 984 had been ordered, initially in London, then elsewhere.
The Changing of the Guard ceremony at Buckingham Palace, a draw for tourists, was canceled because it requires support from police officers, which authorities decided was not a good use of police resources given the threat level.
Rudd also scolded U.S. officials for leaking details about the investigation into the Manchester attack before British authorities were prepared to go public.
British-born Abedi, 22, blew himself up on Monday night at the Manchester Arena indoor venue at the end of a concert by U.S. pop singer Ariana Grande, attended by thousands of children and teenagers.
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.
Greater Manchester Police said they were now confident they knew the identity of all the people who lost their lives and had made contact with all the families. They said they would formally name the victims after forensic post-mortems, which would take four or five days.
The bombing also left 64 people wounded, of whom 20 were receiving critical care for highly traumatic injuries to major organs and to limbs, a health official said.
UNLIKELY ABEDI ACTED ALONE
"It seems likely, possible, that he (Abedi) wasn't doing this on his own," Rudd said on BBC radio. She said Abedi had been known to security services before the bombing.
The BBC reported that the security services thought Abedi may have been a "mule" for a bomb made by someone else, because they thought the device was too sophisticated for him to have put together by himself.
Asked about reports that Abedi had recently returned from Libya, Rudd said she believed that had now been confirmed.
French Interior Minister Gerard Collomb said British investigators had told French authorities Abedi had probably traveled to Syria as well.
"Today we only know what British investigators have told us -- someone of British nationality, of Libyan origin, who suddenly after a trip to Libya, then probably to Syria, becomes radicalized and decides to carry out this attack," Collomb told BFMTV.
Asked if he believed Abedi had the support of a network, Collomb said: "That is not known yet, but perhaps. In any case, (he had) links with Daesh (Islamic State) that are proven."
Islamic State, now being driven from territories in Syria and Iraq by Western-backed armed forces, claimed responsibility for the Manchester attack, but there were contradictions in its accounts of the action and a telling lack of detail.
Prime Minister Theresa May announced late on Tuesday that the official threat level had been raised to its highest level for the first time in a decade, meaning an attack could be imminent.
The UK Independence Party was the first party to announce it would resume campaigning. It plans to unveil its policy pledges on Thursday.
WASHINGTON REBUKED OVER LEAKS
Abedi was born in Manchester in 1994 to parents of Libyan origin, according to U.S. sources citing British contacts.
As Collomb was speaking in France, Rudd was asked by the BBC about the fact that information about Abedi, including his name, had come out from the United States and whether she would look again at how information was shared with other countries.
"Yes, quite frankly. I mean 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."
Asked whether the U.S. leaks had compromised the investigation, she 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."
France, which has repeatedly been hit by devastating militant attacks since 2015, extended emergency powers after the Manchester bombing.
It 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.
Attacks in cities including Paris, Nice, Brussels, St Petersburg, Berlin and London have shocked Europeans already anxious over security challenges from mass immigration and pockets of domestic Islamic radicalism.