Security services have prevented seven attacks in the last six months, David Cameron said as he warned a Paris-style attack "could happen here".
The Prime Minister is meeting Vladimir Putin on the fringes of the G20 summit in Turkey as Western allies try to persuade the Russian president to co-operate in the international struggle against terror group Islamic State (IS) in the wake of attacks in Paris and Egypt.
Mr Cameron said he hoped the talks with the Russian president will be "positive" and said there were hopeful signs that a political solution could be found but admitted there would be "compromises".
The terror spree in France "was the sort of thing we warned about" in planning with the security services but such atrocities meant "you have to go right back to the drawing board" to work out what more steps needed to be taken, he said.
Asked if Britain was at war with IS, the premier said the UK stands in "total solidarity" with France and would do "everything we can" to defeat the jihadis.
The Prime Minister indicated he wanted to speed up plans for introducing new spying powers under the draft Investigatory Powers Bill, telling BBC Radio 4's Today programme "we should look at the timetable".
He added: "We have been aware of these cells operating in Syria that are radicalising people in our own countries, potentially sending people back to carry out attacks.
"Our security and intelligence services have stopped something like seven attacks in the last six months, albeit attacks planned on a smaller scale."
Mr Cameron said he will not hold a vote on extending British military action into Syria until he knows he has the support to get it through because failing would be "damaging" for Britain's "reputation in the world".
He said: "Isil don't recognise a border between Iraq and Syria and neither should we. But I need to build the argument, I need to take it to Parliament, I need to convince more people."