British Prime Minister Theresa May announced on Tuesday evening that the UK's terror threat level has been raised to critical, meaning an attack is expected imminently.

Her announcement follows the suicide bombing in Manchester on Monday night, in which 22 people were killed following a concert.

May made the announcement after a meeting of Cobra, the government's crisis response committee.

"It is a possibility that we cannot ignore that there is a wider group of individuals linked to this attack," she said, adding that raising the level to critical means that military personnel could be deployed to support armed police officers - part of a plan known as Operation Temperer.

"The change in the threat level means there will be additional support available to the police as they work to keep us safe. Operation Temperer is now in force," said May.

Earlier on Tuesday, British police identified the suspected Manchester suicide bomber as 22-year-old Salman Abedi.

Abedi was born in Manchester in 1994 to parents of Libyan birth, U.S. security officials said, citing British intelligence officials.

The Islamic State (ISIS) claimed responsibility for Monday’s attack in Manchester, as it has done for many other attacks that have taken place in Europe in recent years.

Authorities are now trying to determine if Abedi was part of a larger network of ISIS-inspired terrorists.