David Cameron has revealed British intelligence agencies have prevented seven terrorist attacks on Britain in the last six months.
Downing Street said on Monday morning that one of the attacks that had been prevented was stopped in the last two months.
The prime minister told BBC Radio 4's Today programme on Monday morning a Paris-style attack could happen in the UK and it meant Western intelligence agencies would have to go "back to the drawing board" to examine how to tackle the threat.
"This is the struggle of our generation. This disease of Islamist extremist violence, this perversion of the religion of Islam that is being carried out by this minority, is a challenge we will have to face with everything we've got," he said.
Cameron said the attacks stopped in Britain were planned on a "smaller scale" than what happened in Paris on Friday but warned it was a "very dangerous world".
"We have been aware obviously of these cells operating in Syria that are radicalising people in our own countries, potentially sending people, back to carry out attacks," he said.
"Those attacks in Paris, it could have happened in Belgium, it could have happened in Denmark, it could have happened in Sweden, it could happen here."
This morning the prime minister announced the government will hire almost 2,000 extra spies as part of its effort to combat the threat from terrorism.
Cameron is meeting Vladimir Putin as Western allies try to persuade the Russian president to co-operate in the international struggle against terror group Islamic State in the wake of attacks in Paris and Egypt.
Cameron's talks with Putin will be followed by a meeting of the Quint - an informal group of Western powers within the G20, made up of the UK, US, France, Germany and Italy - to assess progress and discuss how further efforts on Syria can be co-ordinated.
The leaders will observe the international minute's silence for Paris at 11am UK time.
The French air force launched a "massive" air strike on the city of Raqqa on Sunday, the capital of the Islamic State movement in Syria. Twelve aircraft including 10 fighter jets targeted a jihadi training camp and a munitions dump, where the Paris massacre was planned, according to a dispatch from Iraqi intelligence officials.
Some 20 bombs were dropped, marking the biggest air strikes by French forces since the country extended its bombing campaign against the extremist group to Syria in September. According to a French Defense Ministry statement, jets were launched from Jordan in coordination with US forces in the Persian Gulf.
In France, police continued their hunt for more members of the sleeper cell that carried out the attacks that killed 129 people on Friday. On Sunday, authorities posted an arrest warrant for Salah Abdeslam, a 26-year-old born in Brussels, wanted in connection with the killings.
French police on the Belgian border stopped a car carrying Abdeslam on Saturday, but let him go. Authorities later identified Abdeslam as the renter of Volkswagen Polo that carried hostage takers to the Paris theater, the scene of the greatest number of fatalities. Abdeslam is one of three brothers believed to be involved; One who crossed with him into Belgium was later arrested, and another blew himself up inside the Bataclan theater after taking the audience hostage and firing on them repeatedly.
HUFFPOST FRANCE: Full Coverage From Paris
On Sunday, Iraqi intelligence officers revealed they had warned coalition countries, and France specifically, of an impending Islamic State attack a day before Friday’s killings. The dispatch sent to western nations said an attack by ISIS was imminent. The coordinated assault on the French capital killed 129 people and left hundreds injured.
According to the Associated Press, the attack was ordered by ISIS leader Abu Bakr al-Baghdadi, who demanded reprisals against the coalition countries currently fighting the group in Iraq and Syria “through bombings or assassinations or hostage taking in the coming days.”
Four Iraqi intelligence officials said they warned France specifically of a likely attack, though the Iraqis said they had no details as to when or where the attack would take place. However, a French security official moved to play down the warning on Sunday, telling AP this was the type of communication they receive "all the time."
The dispatch was shown to an AP reporter on Sunday. Two officials, who spoke under condition of anonymity, said the dispatch included details of how the plan was hatched in Raqqa, Syria, with attackers trained specifically for an attack on France. They were sent to Europe where they contacted a sleeper cell, which was to aid with their operation.
On Saturday, ISIS claimed responsibility for the attacks on the Stade de France, the Bataclan and Paris cafes. Seven of the assailants were killed, six by detonating suicide vests. Police shot one attacker, while an eighth suspect remains at large.