The UK has raised its terror threat level from severe to critical tonight.
The Prime Minister Theresa May has warned another attack may be imminent.
She said it is possible that there is a "wider group of individuals" responsible for the attack in Manchester last night.
She added that armed forces will be deployed on the streets and at strategic sites to support police as part of the ongoing security operation.
UK agencies have been working today to discover who was responsible for the attack at Manchester Arena which killed 22 and injured 120 more at the Ariana Grande concert last night.
A key question is whether he was working alone or as part of an organised terror cell.
A "critical" threat level means an attack is expected "imminently".
In her statement tonight at Downing Street, Mrs May said "The spirit of Manchester and the spirit of Britain is far mightier than the sick plots of depraved terrorists. This is why terrorists will never win and we will prevail."
