Even as the British Police identified the suicide bomber behind the attack at Manchester Arena the government raised the terror threat level from “severe” to “critical”, reported BBC. Prime Minister Theresa May said “critical” level of terror threat means further attacks might be imminent. The decision to raise the terror threat level came as investigators were unable to determine whether suspect Salman Abedi had acted alone in the suicide attack that killed 59 people.

“Our priority, along with the police counter-terrorism network and our security partners, is to continue to establish whether he was acting alone or working as part of a wider network,” Manchester Police Chief Constable Ian Hopkins told Reuters. May also said security at key sites or public events will be boosted and asked public not to be “unduly alarmed”. Military personnel may also be deployed at public events such as concerts or sports events, she added.

Salman Abedi, 22, is believed to be a man of Libyan origin who was a resident of Manchester. Greater Manchester Police said they would share more details once the coroner confirms the accused’s identity. The prime minister had condemned the “cowardice” of the attacker and praised those who offered help.

“The spirit of Britain...a spirit that through years of conflict and terrorism has never been broken and will never be broken,” May had said. The prime minister added that the attacker deliberately chose the concert to cause “maximum carnage”.

The explosion in the arena took place when American singer Ariana Grande was performing. Majority of the audience consisted of teenage fans of the singer. The Islamic State had claimed responsibility for the attack on Monday via a messaging app, Telegram.

The security threat level has reached the highest in the UK only twice in the past. Monday’s attack took place just two weeks before Britain votes in a general election.