In the Commons, Defence Secretary Michael Fallon began laying out the case for extending RAF air strikes into Syria, telling MPs that was where IS organised and directed its operations.
He made clear however that the government would not stage a new vote of MPs unless it was clear there was “some consensus” across the House for widening the existing RAF operations against IS in Iraq.
With senior Conservative MPs continuing to voice their opposition, the support of Labour is crucial if ministers are to be sure of a Commons majority.
In a reversal of its previous position last September when Ed Miliband made clear they would block strikes on Syria shadow defence secretary Vernon Coaker said Labour would “carefully consider” any new proposals from the government.
Nevertheless, with a leadership contest ongoing, the signs are that Mr Cameron will wait until September when a successor to Mr Miliband is in place before going back to the Commons with a new motion.
The prime minister is determined to avoid a repeat of the 2013 vote on military action against Syrian president Bashar al-Assad when he suffered a damaging Commons defeat at the hands of Labour and rebel Conservative MPs.
Mr Cameron’s official spokeswoman said there was a need for “more thought, more deliberation, more time” before any decision was taken, although she stressed that he still believed that ultimately IS had to be dealt with in Syria.
“The prime minister has long thought that Isil poses a threat to Britain and Isil needs to be destroyed in Syria as well as in Iraq,” she said.
“The prime minister’s views haven’t changed. What has changed is the growing evidence that Isil represents a threat to Britain and our national security,” he said.
With some Tories questioning the legal basis of strikes on Syrian territory, she said the government was satisfied a case for action had been established last year when the US-led coalition began air strikes.
She pointed out that the UK was already engaged, providing reconnaissance and air-to-air refuelling capacity for the Syrian operation.