UK National Terror Threat Raised To Highest Possible Level After Manchester Attack: What Critical Alert Means

The United Kingdom raised its national terror threat level from severe to critical Tuesday. MI5, the nation’s domestic security service, escalated the alert to the highest possible level following the bombings at a concert in Manchester Monday evening.

A critical level alert means “an attack is expected imminently,” according to the security force’s guidelines.

In escalating the threat, security judged available intelligence, terrorist capability, terrorist intentions and an analysis of the likelihood of an attack in the near term. The threat level does not have an expiration date but is subject to regular review.

The last time the terror threat in the U.K. was at a critical level was in June 2007 after an attempted car bombing at the Glasgow airport. Prior to that, the terror threat was at a critical level in August 2006 when police arrested 21 people in connection with a plot to bomb a plane flying from the UK to the United States.

The increased terror threat level in the UK came less than a day after a suicide bombing at the Manchester Arena during an Ariana Grande concert. At least 22 people were killed and an additional 50 were injured in the attack.

Police identified 22-year-old Salman Abedi as the bomber who died at the scene of the attack. The Islamic State came forward Tuesday to claim responsibility for the bombing, saying that the perpetrator was one of its "soldiers." U.S. officials said they had not yet verified claims that ISIS was responsible.

"We struggle to comprehend the warped and twisted mind that sees a room packed with young children not as a scene to cherish but as an opportunity for carnage," Prime Minister Theresa May said in a statement. "But we can continue to resolve to thwart such attacks in the future, to take on and defeat the ideology that often fuels this violence. And if there turn out to be others responsible, to seek them out and bring them to justice."

May said the terror level was escalated because security had not yet ruled out the possibility that additional people could be linked to the attack. A European intelligence official cited by the Washington Post said the brother of the suspect was taken into custody following the attack.

"We believe at this stage the attack was conducted by one man," Greater Manchester Police Chief Constable Ian Hopkins said in a statement. "We believe the attacker was carrying an improvised explosive device, which he detonated, causing this atrocity."

Hopkins noted that the police were working to determine whether the suspect was acting alone or as part of a network.