UK Prime Minister Theresa May said police and security staff believe they know the identity of the attacker behind Monday's blast in Manchester that killed 22 people, but are remaining tightlipped over the details. 

May, speaking from Downing Street, said a single terrorist detonated an improvised explosive device near the exit of Manchester Arena as concertgoers were leaving a show.

Calling the attack "one of the worst" terror incidents the UK has suffered ever, she added: "Our values, our country and our way of life will always prevail."

The British prime minister also said the threat level to the UK remains at severe, and she will chair another security meeting later on Tuesday.

At least 22 people, including children, were killed and nearly 60 others injured after the explosion in Manchester on Monday night local time.

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