British Prime Minister Theresa May raised the UK's terror threat level from severe to critical on Tuesday evening, meaning that another attack in the UK could be imminent. Critical is the highest of the five levels devised by the intelligence services.

May's announcement, made in a live television statement, follows a suicide bombing at Manchester Arena on Monday evening which killed 22 and injured 59 at the end of a pop concert starring US star Ariana Grande. Many of the dead were children.

The UK's terror threat level is now at its highest since 2014, as the British police continue to investigate links between suicide bomber Salman Abedi and terror groups.

"It is a possibility that we cannot ignore that there is a wider group of individuals linked to this attack," May said.

Raising the level to critical means that military personnel could be deployed to support armed police officers.

"The change in the threat level means there will be additional support available to the police as they work to keep us safe," she said.

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