The UK terror threat has been raised to critical in the wake of the Manchester suicide bombing attack amid fears attacker Salman Abedi did not act alone.
Monday night's attack at an Ariana Grande concert left 22 people dead and injured 59. Some 20 people are being treated for "horrific injuries" in critical care and 12 of those rushed to hospital were children.
Military troops are set to bolster police forces after Prime Minister Theresa May raised the threat level to the highest possible rating, meaning another atrocity is expected imminently.
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Theresa May said a "wider group of individuals" could have been involved in the Manchester Arena blast rather than just suicide bomber Abedi.
In a sign of the increased threat, the military could be deployed to support armed police officers, Ms May added during a live televised statement from Downing Street.
Monday night's attack at a concert by US pop star Ariana Grande left 22 people dead, including an eight-year-old girl, and dozens injured.
Isis has claimed responsibility for the barbaric attack, which involved a home-made device packed with nuts and bolts which exploded in the venue's foyer as thousands of young people were leaving.
Abedi, believed to have been born in Manchester and of Libyan descent, has been named as the suicide bomber.
The 22-year-old studied business at Salford University but dropped out before completing his degree.
He is thought to have attended the Manchester Islamic Centre, also known as Didsbury Mosque, along with his parents and siblings.
Elsewhere in the city, the first arrest was made in connection with the inquiry when a 23-year-old man was detained near a Morrisons in Chorlton.
The terror threat level was increased after investigations revealed he may not have acted alone.
Ms May said Operation Temperer - allowing military personnel to take to the streets - is now in force.
Counter-terrorism agencies have mounted a massive inquiry into the outrage - the worst terrorist attack since 52 innocent people were killed in the July 7 bombings in London in 2005:
