The British Prime Minister, Mrs. Theresa May, has said that the United Kingdom terror threat level has been raised to the highest level of “critical,” meaning further attacks may be imminent.

The revelation, it was gathered, came after investigators were unable to rule out Manchester bombing suspect Salman Abedi acted alone.

Twenty-two people were killed and 59 injured on Monday night when a suicide bomber attacked concert-goers at Manchester Arena where a United States pop singer, Ariana Grande was billed to perform.

May said military personnel would now be deployed to protect key sites, adding that military personnel might also be seen at other events, such as concerts, and would work under the command of police officers.

Reacting to the attack outside her Downing Street office, after a meeting with security and intelligence chiefs, May disclosed that the police believed they knew the identity of the bomber.

Describing all terrorist acts as “cowardly,” she was quoted by Reuters as saying that “this attack stands out for its appalling sickening cowardice, deliberately targeting innocent, defenceless, children and young people who should have been enjoying one of the most memorable nights of their lives.”

The prime minister also said security services were working to see if a wider terror group was involved in the attack.