THERESA May has chaired another COBRA meeting this morning after raising the terror threat level to critical as the Army hits the street to help out following the horrific Manchester bombing.

It comes amid fears another attack could be imminent as investigators continue to probe links suicide bomber Salman Abedi may have to terror groups.

22 Theresa May has said the threat level has been raised to critical and that the Army will support cops

22 Amber Rudd said today the operation was making 'good progress' Credit: Getty Images

22 Foreign Secretary Boris Johnson arriving in Downing Street today Credit: SWNS:South West News Service

22 Police raid the home of Brit national Salman Abedi after the Manchester Arena nail bomb attack Credit: Eamonn and James Clarke

22 Salman Abedi was 'known' to police, said Amber Rudd Credit: The Sun

Army have taken over manning the sentry boxes at Parliament from the cops. pic.twitter.com/Mew9FpXtF8 — Harry Cole (@MrHarryCole) May 24, 2017

The army are set to stand guard outside Buckingham Palace, Westminster and Downing Street. Some have already been sent to Parliament today.

Amber Rudd said this morning following the COBRA meeting that "good progress" has been made on the operation, which included "a number of arrests overnight. That will continue."

And she said: "The Prime Minister chaired the emergency committee meeting this morning and we learned about the fantastic work that is being done locally in Manchester."

The Home Secretary confirmed that the army would be on the streets today: "Today we have 984 members of the military coming forward as requested by the police.

"They will be initially deployed in London but then to the rest of the country as requested."

After meeting with security chiefs last night the Prime Minister said Britain will never be defeated by terrorism.

She once again praised the response to Monday night's brutal slaying at Manchester Arena, which killed 22 concert-goers and maimed 59.

Mrs May said: "I want to reiterate what I said this morning about the professionalism of the emergency services and the bravery of the people of Manchester.

“Through their actions, they proved that cowardice will always be defeated by bravery, that evil can be overcome by good, and that our values - the liberal, pluralistic values of Britain - will always prevail over the hateful ideology of the terrorists.”

She said: “And while we mourn the victims of last night’s appalling attack, we stand defiant.

“The spirit of Manchester - and the spirit of Britain - is far mightier than the sick plots of depraved terrorists.

“That is why the terrorists will never win, and we will prevail.”

22 One man wielding a knife was arrested near Buckingham Palace this morning - not thought to be terror-related Credit: PA:Press Association

22 Armed police outside No 10 Downing Street this morning Credit: EPA

22 Extra security will be deployed - including the army Credit: PA:Press Association

22 Police standing guard outside the Palace of Westminster Credit: PA:Press Association

Raising the terror threat, which had been at severe since 2014, to critical, means security services are expecting another attack imminently.

Explaining the decision the PM said police and security services needed to investigate whether or not Abedi was acting alone.

The PM added: “But the work undertaken throughout the day has revealed that it is a possibility we cannot ignore that there is a wider group of individuals linked to this attack.”

And this morning the Home Secretary Amber Rudd confirmed the 22-year-old was known "up to a point" to the intelligence services - and that it was likely he wasn't acting alone.

22 The PM wrote a message in the book of condolence in Manchester last night Credit: PA

22 She wrote after 22 people were murdered in the horrific attack at the Ariana Grande concert Credit: PA

Mrs May said the police asked for authorisation from the Secretary of State for Defence to place armed military personnel at key sites around the country, which was approved.

This will include Downing Street, Buckingham Palace and other areas around Westminster.

The soldiers will be deployed as part of Operation Temperer, with the PM announcing that they will be "visible" at large events including concerts and football matches.

This is the first time Operation Temperer, set up after the Charlie Hebdo terror attack in Paris in January 2015, has been mobilised.

The PM said: “I do not want the public to feel unduly alarmed. We have faced a serious terrorist threat in our country for many years.

“And the operational response I have just outlined is a proportionate and sensible response to the threat that our security experts judge we face.

“I ask everybody to be vigilant, and to cooperate with and support the police as they go about their important work.”

22 Theresa May said a police request for military support has been approved Credit: Mercury Press

22 An injured woman is escorted from the arena by police after loud bangs were heard at the gig Credit: London News Pictures

22 A female police officer comforts a young fan after the atrocity Credit: Cavendish Press

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What do the threat levels mean? Threat levels are designed to give a broad indication of the likelihood of a terrorist attack. LOW means an attack is unlikely.

means an attack is unlikely. MODERATE means an attack is possible, but not likely

means an attack is possible, but not likely SUBSTANTIAL means an attack is a strong possibility

means an attack is a strong possibility SEVERE means an attack is highly likely

means an attack is highly likely CRITICAL means an attack is expected imminently

And Assistant Met Commissioner Mark Rowley, the country's National Counter Terrorism Policing lead, later confirmed the decision was taken due to "gaps in our knowledge" as officers continue to chase down leads.

Mrs May confirmed the death count from the atrocity remains at 22 but said that many others have life-threatening injuries.

As the announcement was made last night, thousand's gathered in the Manchester Albert Square for a vigil to those caught up in the carnage and landmarks around the world were lit in red, white and blue in an act of solidarity.

London Mayor Sadiq Khan said everything was being done to protect the city as the terror threat was raised.

In a statement he said: "There will be additional police officers on London's streets over the coming days - including additional armed officers.

"You will also see some military personnel around London - they are there to help our police service to keep us safe and guard key sites.

"London stands in solidarity with the people of Manchester.

"Those who seek to harm and divide us through barbaric acts of terrorism will never succeed. We will never be cowed by terrorism."

From 'severe' to 'critical' Theresa May's speech after chairing a COBRA meeting last night: "I have just chaired another meeting of COBR, where we again discussed the callous and cowardly terrorist attack in Manchester last night, and the operational response from the security service, the police and other emergency services.

"It remains the case that, other than the terrorist himself, 22 people were killed in the attack. Fifty-nine people remain injured, and many of them have life-threatening conditions.

"As Greater Manchester Police confirmed earlier today, the perpetrator was Salman Ramadan Abedi, a 22-year-old who was born and brought up in Britain.

"And as the emergency services have confirmed throughout the day, his victims were innocent children, young people and their families.

"Our thoughts and prayers are with them all.

"I want to reiterate what I said this morning about the professionalism of the emergency services and the bravery of the people of Manchester.

"Through their actions, they proved that cowardice will always be defeated by bravery, that evil can be overcome by good, and that our values - the liberal, pluralistic values of Britain - will always prevail over the hateful ideology of the terrorists.

"In my statement earlier today, I said that the police and security services needed to investigate whether or not Abedi was acting alone. Those investigations continue.

"But the work undertaken throughout the day has revealed that it is a possibility we cannot ignore that there is a wider group of individuals linked to this attack.

"This morning, I said that the Joint Terrorism Analysis Centre (JTAC) - the independent organisation responsible for setting the threat level on the basis of the intelligence available - was keeping the threat level under constant review.

"It has 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.

"The change in the threat level means that there will be additional resources and support made available to the police as they work to keep us all safe.

"As a result of the JTAC’s decision, the police have asked for authorisation from the Secretary of State for Defence to deploy a number of armed military personnel in support of their armed officers.

"This request is part of a well-established plan, known as Operation Temperer, in which both the armed forces and the police officers involved are well-trained and well-prepared to work in this kind of environment.

"The Secretary of State for Defence has approved this request, and Operation Temperer is now in force.

"This means that armed police officers responsible for duties such as guarding key sites will be replaced by members of the armed forces, which will allow the police to significantly increase the number of armed officers on patrol in key locations.

"You might also see military personnel deployed at certain events, such as concerts and sports matches, helping the police to keep the public safe.

"In all circumstances, members of the armed forces who are deployed in this way will be under the command of police officers.

"Precisely how the military and armed police officers will be deployed is an operational decision for police commanders and Assistant Commissioner Mark Rowley of the Metropolitan Police will be making a statement giving further details at New Scotland Yard later this evening.

"In the coming days and weeks, there will of course be many events hosted up and down the country. The police will work with the organisers and hosts of these events, to come to a judgement about how they can go ahead while making sure the people who attend them are safe and secure.

"I do not want the public to feel unduly alarmed. We have faced a serious terrorist threat in our country for many years.

"And the operational response I have just outlined is a proportionate and sensible response to the threat that our security experts judge we face. I ask everybody to be vigilant, and to cooperate with and support the police as they go about their important work.

"I want to end by repeating the important message I gave in my statement earlier today. We will take every measure available to us and provide every additional resource we can to the police and the security services as they work to protect the public.

"And while we mourn the victims of last night’s appalling attack, we stand defiant. The spirit of Manchester - and the spirit of Britain - is far mightier than the sick plots of depraved terrorists. That is why the terrorists will never win, and we will prevail."

22 Prime Minister Theresa May with Greater Manchester Police chief constable Ian Hopkins on Tuesday Credit: Getty Images

22 An injured man is led from the arena in Manchester after the chaos Credit: London News Pictures

22 Dozens were injured in the terror attack Credit: Cavendish Press

22 An injured fan is led away from the carnage Credit: London News Pictures

Brit-born 22-year-old Manchester United fan Abedi was named as the suspect behind the bombing.

MI5 spooks and anti-terror cops are now racing against the clock to uncover his links to any possible terror cell and discover if he was groomed for the atrocity.

Officers raided his home in Fallowfield, Manchester and another address, as well as arresting a 23-year-old man in Chorlton.

Details of the horrific attack emerge as:

Among the university dropout's victims were eight-year-old Saffie Rose Roussos, John Atkinson, Kelly Brewster and Georgina Callander, 18, who were all killed after a huge bomb, thought to be packed with nails and bolts, exploded as the gig ended.

Details are already beginning to emerge about the killer, who was known to MI5, with neighbours speaking of his "strange behaviour" in the weeks leading to the attack.

Sources said the aim of investigators would be to establish if Abedi himself had built the deadly device - or if a bomb-making mastermind was behind the blast.

A source told The Sun: "Attacks like this are mercifully rare because they require expertise - or a great deal of luck - to pull off.

"In this case the real fear is that Abedi was just the tip of a more sinister network.

"The focus will now be on his friends, family and other ties to see if there was a sprawling terrorist network behind him."

ISIS fanatics have already boasted of the sickening attack, claiming even more "severe" plots would be unleashed in Britain.

22 The blast detonated in the box office as thousands of pop fans left the concert, many going to Victoria station

22 Wounded people on Hunts Bank outside Victoria Station Credit: London News Pictures

22 Witnesses reported thousands of screaming fans ran from the concert hall as armed police were called in Credit: London News Pictures

Abedi's attack on the 21,000-strong crowd at Monday night's Ariana Grande concert killed 22 and left a further 59 injured.

Twelve children under 16 were taken to hospital in a critical condition, with many of the dead also feared to be youngsters.

Among the many dead is pop fan Georgina Callander, 18, who has yesterday been described as a girl who “lit up the room”.

She had tragically written to her pop hero the day before the attack, telling the pop star: “SO EXCITED TO SEE U TOMORROW”.

A close friend told the Evening Standard she died with her mother at her hospital bedside.

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Eight-year-old Saffie Rose Roussos was revealed as the second victim of the blast.

Saffie, of Leyland, Lancs, was killed after becoming separated from her mum and sister during the attack.

The mum of the tragic youngster is reportedly fighting for her life with no idea her daughter did not survive the attack.

John Atkinson, 26, of Radcliffe, Greater Manchester, has also been named in reports as one of the 22 killed.

One friend posted on the internet: “Truly devastated for them all. What an amazing lovely man he was and blessed to have known him.xxx”

Brave Kelly Brewster, 32, of Sheffield, who shielded her niece from the deadly blast was named as the fourth victim.

SHOW YOUR SUPPORT FOR THE VICTIMS OF THE MANCHESTER ARENA ATTACK Yesterday we launched a Together With Manchester appeal – to raise money for families of the victims of the Arena bomb. News UK, publisher of The Sun, has made a corporate donation of £100,000 to the appeal. Here's how you can show your support.... ONLINE: www.justgiving.com/TogetherWithManchester TEXT: Text TWMC50 and amount to 70070 – eg TWMC50 £5

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In the aftermath of the explosion youngsters struggled to get home with the city's kindhearted residents offering places to stay and taxi drivers giving free trips.

The attack was slammed by the Muslim Council of Britain, with the community banding together in support for the victims and their families.

Dozens of bouquets, toys and posters have been laid in Manchester as the city grieved for the victims, with kind-hearted strangers offering up chocolates and sweets to those injured.

Police have upped their presence on the streets of London in response to the attack.

In a statement, the Queen expressed her "deepest sympathy" and added: “The whole nation has been shocked by the death and injury.”

The attack came on the fourth anniversary of the murder of British soldier Lee Rigby and just two months after four were slaughtered when a Hyundai 4x4 driver mowed down people on Westminster Bridge, central London.

If you’re concerned about suspicious behaviour call the Anti-Terrorist Hotline on 0800 789 321