Terror threat level raised from 'severe' to 'critical' after Manchester Arena attack

The UK terror threat level has been raised from severe to critical - the highest possible - after the Manchester Arena bombing.

The move indicates that another attack could be "imminent", as well as "highly likely".

After chairing a meeting of the Government's emergency COBRA committee, Theresa May announced the change, saying military personnel will help armed police officers guard key sites.

:: LIVE: The latest updates on the Manchester attack from the Paste BN team

Under Operation Temperer, members of the armed forces could be deployed to public events, such as concerts and sports events, and also on the streets and at major shopping centres.

Twenty-two people were killed and 59 others injured when a bomber blew himself up in the arena foyer as thousands of concertgoers were leaving after a gig by US pop star Ariana Grande.

The suspect has been named by police as Salman Abedi, and investigations have revealed he may not have acted alone.

Islamic State has claimed it carried out the attack, which involved a homemade device packed with nuts and bolts.

:: Eight-year-old Saffie Roussos named as Manchester bomb victim

The Prime Minister said the possibility "that there is a wider group of individuals linked to this attack" could not be ignored.

Mrs May said the Joint Terrorism Analysis Centre - the independent body which sets the threat level - had recommended it be raised after the bombing on Monday evening.

She said: "It is 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."

:: Singer Ariana Grande 'broken' by bombing of young fans

Please use Chrome browser for a more accessible video player

2:33

Assistant Commissioner Mark Rowley, head of national counter-terrorism policing, said the investigation was "making good progress".

He said: "There has been an arrest and there are currently multiple searches and other activity taking place as I speak.

"The public would expect the police to do everything possible to prevent further attacks and keep them safe.

"We are flexing our resources to increase police presence at key sites, such as transport and other crowded places and we are reviewing key events over the coming weeks."

:: Bomb attack witness: 'It was absolute carnage'

Please use Chrome browser for a more accessible video player

2:04

Following the increase to the threat level, all the major political parties have cancelled General Election campaigning for a second day.

It is not yet known how long the suspension - which covers campaigning on both a local and national level - will last.

This attack is the worst terrorist incident ever during a general election period.

It is the first time in a decade that the terror threat level has been at critical.

Please use Chrome browser for a more accessible video player

1:47

The last occasions were in August 2006 and June 2007, the latter following the Glasgow airport attack. Both times, the assessment was lowered after a few days.

Police investigating the arena attack have arrested a 23-year-old man.

Threat levels are designed to give a broad indication of the likelihood of a terrorist attack.

:: LOW means an attack is unlikely

:: MODERATE means an attack is possible, but not likely

:: SUBSTANTIAL means an attack is a strong possibility

:: SEVERE means an attack is highly likely

:: CRITICAL means an attack is expected imminently

:: A hotline has been set up for those with concerns about loved ones who remain unaccounted for. Those worried about their friends or family should call 0800 096 0095.