MANCHESTER, England -- Three more people have been arrested in connection with the Ariana Grande concert attack, according to Sky News.
Police have already named Salman Abedi, a British-born national of Libyan descent, as the bomber in the attack on Manchester Arena, which killed at least 22 people, including children. Abedi died in the blast, in what appears to have been a suicide bombing.
Monday's blast marked the deadliest terror attack on British soil since the 2005 London bombings. ISIS claimed responsibility for the bombing Tuesday morning.
"The intelligence services know a lot of people, and I'm sure we will find out more what level they knew about him in due course, but at the moment all they have confirmed is that they did know about him. And as I say, we will find out more when the operation is complete," she said.
Prime Minister Theresa May announced Tuesday night that Britain's threat level had been raised from "severe" to "critical," and warned that a "further attack may be imminent."
Children among the dead
Six people who died in the horrific attack have been identified -- they include an 8-year-old girl and two teenagers.
Concertgoer Olivia Campbell, 15, whose mother spoke to CNN during an agonizing wait for news from her daughter, had gone to the concert with her friend Adam to celebrate his birthday.
"RIP my darling precious gorgeous girl Olivia Campbell taken far far to soon go sing with the angels and keep smiling mummy loves you so much," Charlotte Campbell wrote, posting a Snapchat photo of her daughter.
Eight-year-old Saffie Rose Roussos from Leyland was also named as one of the fatalities, Lancashire County Council confirmed.
Chris Upton, the head teacher at the Tarleton Community Primary School, described her as "simply a beautiful little girl" who was "quiet and unassuming with a creative flair."
Two Poles were also named among the dead, according to a tweet from Poland's Foreign Ministry. No further details have been released.
Georgina Callander, 18, a superfan who had met Ariana Grande, was killed, according to her school, and John Atkinson, a 26-year-old student from the Greater Manchester area also died in the attack, according to Ivan Lewis, a local politician.
At least 12 victims aged 16 or under were being treated at a children's hospital for serious injuries, some of them fighting for their lives, a Manchester health official said.
On Tuesday evening, hundreds attended a vigil outside Manchester City Hall in honor of the victims.
"We will stand together to say that this city is greater than the force that aligns itself against it," David Walker, Bishop of Manchester, told the crowd.
"We are sending a signal not just to Manchester, but across the world that you can not defeat us because love in the end is always stronger than hate."
The city remained defiant in the face of one of the deadliest terror attacks the UK has faced. Mayor Andy Burnham said Tuesday that it would be "business as usual, as far as possible, in our great city."
A cafe owner said that the city's sense of community was helping people come together during the difficult time.
"We're only here to express some positivity and to be here for our community. We're offering free food and drink, and shelter for all that are stranded that need help."
The pop star has suspended her "Dangerous Woman" tour following the attack, a source with knowledge of the situation told CNN. Grande was scheduled to perform in London and across Europe through mid-June.