UK raises terror threat to 'critical'

The announcement came a day after a deadly suicide bomb attack targeted a concert venue in Manchester where American pop star Ariana Grande was performing Monday night.

"It has now concluded, on the basis of today's investigations, that the threat level should be increased for the time being from severe to critical. This means that their assessment is not only that an attack remains highly likely, but that a further attack may be imminent," May said.

The terror threat level was raised to critical twice in 2006 and 2007, and lasted a few days.

May confirmed a suspected 22-year-old male suicide bomber was behind the attack that killed 22 victims and injured 59 others in the explosion in the foyer area of the Manchester Arena at the end of the concert that was attended by thousands of children and teens.

The possibility exists others are linked to the suspect and the threat level should be increased to critical, according to the prime minister.

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