London (AFP) - British security services have foiled at least seven terror plots in the past year, with fighters returning from Syria posing a growing threat, Prime Minister David Cameron said Monday.

"Our security services have foiled no fewer than seven different terrorist plots right here in Britain over the past year alone," Cameron said in a speech in London.

"We need to do more to ensure our agencies have the resources and the information they need to prevent and disrupt plots against this country at every stage."

Cameron had earlier said that the plots were foiled in six months, but later clarified that the period was actually a year.

In the wake of attacks in Paris that killed at least 129 people, British security services will have to re-think their strategy to deal with multiple coordinated street attacks, according to the prime minister.

"The more we learn about what happened in Paris the more it justifies the approach that we are taking in Britain," Cameron told the audience at the Lord Mayor of London's Banquet.

"When you are dealing with radicalised European Muslims, linked to ISIL in Syria and inspired by a poisonous narrative of extremism, you need an approach that covers the full spectrum - military power, counter-terrorism expertise and defeating the poisonous narrative that is the root cause of this evil."

Cameron has said that signs of hope emerged from Saturday's talks in Vienna on Syria on how to deal with the Islamic State (IS) group, also known as ISIL.

Cameron added there were "hopeful signs" from Saturday's talks in Vienna on Syria that progress was being made on how to deal with the Islamic State (IS) group.

But he has stressed that any settlement must include the removal of Syrian President Bashar al-Assad, a sticking point between the West and Russia.

- 'Generational struggle' -

Britain is to recruit an extra 1,900 security and intelligence staff to counter the threat of terrorist violence following the Paris attacks, as part of the government's five year defence and security review to be unveiled next week.

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It has been described as the biggest increase in British security spending since the 7/7 bombings in London that killed dozens in 2005.

The recruitment would increase the staff of intelligence agencies MI5, MI6 and GCHQ by some 15 percent in order to fight what Cameron called a "generational struggle".

In addition, Cameron announced an additional Â£2 billion ($3 billion, 2.8 billion euros) in spending on the British Army's SAS and other special forces, to new weapons, vehicles and equipment.

More of Britain's aid spending would go towards fragile states, and moderate Muslims in Britain would be helped with funding, protection and political representation, Cameron said.

There will also be a doubling of British funding for aviation security around the world, in response to the crash of a Russian plane in Egypt last month that the British government suspects may have been downed by a bomb.

British media reported the current funding for aviation security at around Â£9.0 million (12.7 million euros, $13.7 million).

Britain is engaged in air strikes against IS in Iraq, but has not joined in the operation over Syria.

Cameron wants to extend the mission, but has acknowledged that work is required to convince opposition politicians in order to get his plan approved.

Speaking in a venue bombed in the Second World War, Cameron said Britain should summon the determination to defeat terrorism that it showed Germany's Adolf Hitler.

"It is that same resolve that will defeat this terrorism and ensure that the values we believe in, and the values we defend, will again in the end prevail," Cameron said.