The Manchester bombing is Britain's second terror attack in two months. The friend has undergone surgery to treat injuries from the bombing.

Abedi is believed to have died in the powerful blast, but he has not yet been formally identified by the coroner, Manchester police said. British soldiers have been deployed in place of police officers to guard high-profile sites such as Buckingham Palace and Parliament.

- The attack was carried out by a lone male suicide bomber who detonated an improvised explosive device.

"The intelligence services know a lot of people, and I'm sure we will find out more what level they knew about him in due course, but at the moment all they have confirmed is that they did know about him".

She said armed police patrols had been increased and will be ready to respond quickly to any incidents.

Many of those still hospitalized had serious wounds that will require "very long term care and support in terms of their recovery", Rouse said.

Britons woke up with the threat level raised to "critical", suggesting another attack remains highly likely and could be imminent.

Following a meeting of the Government's Cobra emergency committee, the Home Secretary said 984 military personnel were being deployed around the country in support of the police.

Omar Alfa Khuri, who lives across the street, said he was awakened at 2:30 a loud noise and saw police take away the father of the family that lives there in handcuffs.

Intelligence experts believe the device detonated at a concert by the pop singer Ariana Grande at the Manchester Arena on Monday night was so sophisticated that Abedi must have either been given specialist training overseas or used a bomb made by a technician who has not yet been captured.

Rudd also scolded US officials for leaking details about the investigation into the Manchester attack before British authorities were prepared to go public.

The presence of troops comes as the United Kingdom raised its threat level to "critical", its highest.

She also complained about USA officials leaking sensitive information about Abedi to the US press.

Abedi lived a short drive from the concert hall, and his attack was claimed Tuesday by the Islamic State group, or ISIS, which said in a statement on the online messaging service Telegram that one of its "soldiers" was responsible, according to the Post.

As of 10.45am on Wednesday - just over 36 hours after the attack - more than £800,000 had flooded into the newspaper's charity page.

Likewise, there have only been two prior instances when the threat level was raised to "critical".