Prime Minister Theresa May has condemned last night's attack in Manchester as an "appalling" and "callous" event.
Speaking outside 10 Downing Street after an explosion at the Manchester Arena killed 22 people, May condemned the targeting of young people attending an Ariana Grande concert, saying the incident "stands out for its appalling, sickening cowardice, deliberately targeting innocent defenceless children and young people".
May said security services believe they have identified the perpetrator of the attack, but are not yet ready to publicly release his identity.
"The police and security services believe the attack was carried out by one man, but they know need to know whether he was acting alone or as part of a wider group. It will take some time to establish these facts," she said.
Earlier this morning May chaired an emergency meeting of the Cobra committee in Downing Street in response to the attacks. A second Cobra meeting will take place later today.
59 people remain injured after last night's attack, and the Prime Minister confirmed that "many" of the injured are children and young people, with "many" of the injured in a life-threatening condition.
May will travel to Manchester to meet the chief constable of Greater Manchester Police, Ian Hopkins, Greater Manchester mayor Andy Burnham and emergency services workers later today.
The UK's largest political parties have all suspended national election campaigning today as a mark of respect.
The explosion happened following the concert at Manchester Arena, with Greater Manchester police called to the scene just after 10.30pm, with surrounding roads closed.
Police believe the attack was carried out by a sole man, who is also believed to have died after triggering an improvised explosive device.
Home secretary Amber Rudd has described the incident as a "barbaric attack, deliberately targeting some of the most vulnerable in our society".
Burnham has also called for a vigil in the city's Albert Square from 18.00 tonight.
It comes almost exactly two months after an armed man killed five people, including one police officer, in an attack in Westminster.