Primer Minister David Cameron has said the terror threat level in the UK remains at ‘severe’ but warned the “horrifying and sickening” terror attack in Paris last night would prompt a review of security measures.

East Anglian Daily Times: Photo: Sky News.Photo: Sky News.

Mr Cameron added he had spoke with French President Francois Hollande, who blamed the Islamic State terror group for the attacks, which killed at least 127 people.

Mr Cameron said in a statement: “The events in Paris are the worst act of violence in France since the Second World War. The worst terrorist attack in Europe for a decade. A horrifying and sickening attack.

“Shocked, but resolute. In sorrow, but unbowed. My message to the French people is simple: Nous sommes solidaires avec vous. Nous sommes tous ensemble. We stand with you. United.

“These were innocent victims enjoying a Friday night out with friends and family, no doubt at the end of a hard week.

“They were not seeking to harm anyone. They were simply going about their way of life – our way of life.

“And they were killed and injured by brutal, callous murderers who want to destroy everything our two countries stand for. Peace. Tolerance. Liberty. But we will not let them.”

Mr Cameron said people must be prepared for British casualties, and that the government would redouble efforts to wipe out the “poisonous extremist ideology”.

He added: “The threat level is already at severe, which means an attack is highly likely, and will remain so.

“This summer police and other emergency services carried out a major exercise to test our response for multiple firearms attacks.

“And in light of last night’s attacks, we will of course review our plans and make sure we learn any appropriate lessons.

“It is clear that the threat from ISIL is evolving. Last night’s attack suggests a new degree of planning and co-ordination and a greater ambition for mass casualty attacks.

“And we must recognise that however strong we are, however much we prepare, we in the UK face the same threat. That’s why we continue to encourage the public to remain vigilant.

“And we will do all we can to support our police and intelligence agencies with the resources and the capabilities they need.

“The terrorist aim is clear. It is to divide us and to destroy our way of life. So more than ever we must come together and stand united. And carry on with the way of life that we love, and that we know, and that will never be moved off.

“Together, we will defeat these terrorists.”

Speaking after an emergency meeting of senior government and security officials at the Elysee Palace, Mr Hollande announced three days of national mourning and vowed that France would be “pitiless” in its response to terrorism.

Mr Hollande, who has cancelled a planned visit to Turkey for the G20 summit this weekend, is to address both houses of the French parliament at Versailles on Monday, when there will be a minute’s silence for victims. The president has spoken with other world leaders by phone, including German chancellor Angela Merkel and Turkish president Recep Tayyip Erdogan.

A manhunt is under way for accomplices of gunmen who targeted a concert hall and the French national football stadium and sprayed the terraces of bars and restaurants with gunfire in at least six separate attacks.

French authorities said they believed all eight of those involved in the attacks were dead - seven of them killed by suicide bombs - but Paris’s chief prosecutor said it was possible other terrorists were still on the run.

Eight attackers died, including seven in suicide bombings, but the city’s prosecutor said it is possible there are still terrorists on the run.

In horrific scenes officers stormed the Bataclan concert hall where hostages were being held but attackers, wearing suicide belts, blew themselves up, leaving 80 people feared dead.

Earlier reports indicated 100 people had been killed inside the venue.

During a visit to the concert hall in the early hours Mr Hollande, who has cancelled his trip to the G-20 meeting in Turkey, said the country will be “merciless” against those who have attacked them.

“We will lead the fight. We will be merciless,” he said.

The national football side was playing a friendly match against Germany at the Stade de France when two suicide attacks and a bombing took place nearby.

President Hollande had been at the stadium but was evacuated. Tens of thousands of people fell silent at the stadium on Friday night in tribute to those killed and injured.

Gregory Goupil of the Alliance Police Nationale said there were at least three dead in the attacks near the stadium. He said the explosions went off simultaneously.

As many as 18 people died when the terrace of the Rue de Charonne was sprayed with gunfire, while around 14 people were killed when Le Carillon bar-cafe, and the nearby Cambodian restaurant Le Petit Cambodge, were also shot at, prosecutor Francois Molins said.

Two hundred people were injured in the string of attacks, French media reported.

Scenes of “carnage” were described by witnesses at the Bataclan, who said there was “blood everywhere”.

World leaders including Barack Obama and David Cameron have spoken of their shock and outrage at the violence.

The Prince of Wales is to send Mr Hollande a message of “profound sympathy and solidarity with the people of Paris”, a Clarence House spokeswoman said

The attacks come after the Charlie Hebdo atrocity, which took place in January and saw 12 people killed after gunmen stormed the offices of the satirical magazine.

They also come a day after Islamic State militant Mohammed Emwazi, known as Jihadi John, was targeted in a US air strike in Syria. It is not clear if there is any link.

President Obama told a press conference that the violence in Paris “was an attack on all of humanity”.

He said: “Those who think they can terrorise the people of France and the values they stand for are wrong.”

Eyewitness Ben Grant said he was in a bar with his wife when the gunshots were fired and he had seen six or seven bodies on the ground.

He told the BBC: “I heard gunshots. People dropped to the ground. We put a table over our heads to protect us.

“We were held up in the bar because there was a pile of bodies in front of us.”

Television cameraman Charles Pitt said he was outside a cafe in the city’s 11th arrondissement where people were shot at around 9.10pm local time.

He told BBC News: “I had literally gone about 30 metres when, I thought it was a firecracker to start with, and then it went on and it got louder.

“It went on for a minute. Everybody dived for cover thinking it was gunfire. Then there was a pause for about 15 seconds and then it all started up again.

“Then it calmed down a bit and I walked back to the front of the cafe and there was a whole pile of bodies, probably about seven on the left-hand side and four that had been sitting on the tables outside on the right-hand side, and a lot of injured.

“I saw a woman who had obviously been shot in the leg.”

The Bataclan concert hall had been due to host a gig by US rock band Eagles Of Death Metal. All of the group have been accounted for and are safe, a US official said.

The Foreign Office advised Britons to “exercise caution in public places” following the attacks and people with concerns about British friends or relatives in Paris can 0207 0081500 for assistance.