A consensus is building behind military action against Islamic State (IS) in Syria, the Government believes, after David Cameron warned that the jihadist group views the UK as a "top tier" target.
The Prime Minister urged MPs to protect the British public by backing air strikes against IS strongholds in Syria as he set out his strategy in the Commons.
No decision on whether to send RAF drones and planes to strike IS targets in Syria will take place until Mr Cameron is sure he has a "clear majority" of MPs in favour.
But Foreign Secretary Philip Hammond told the BBC: "From what I have seen from the response to the Prime Minister's statement today it feels to me that we are building a consensus now for military action in Syria as part of a package of British response which will include a humanitarian and a very strong diplomatic/political strand as well."
A vote could be held as soon as next week, but will require securing a consensus behind action in the Commons, something the Prime Minister believes is essential to avoid handing IS a propaganda victory.
That will depend on persuading Labour MPs to back action - but the party appears deeply split on the issue.
Mr Hammond said the Prime Minister wants to give MPs "a little bit of time" to consider his statement.
"Let's let the dust settle. I'm sure MPs will want to talk to their constituents over the weekend and I think we'll be in a stronger position when parliamentarians return next week to get a sense of whether that crucial consensus has been built."
Labour leader Jeremy Corbyn, who opposed the intervention against IS in Iraq last year, stopped short of saying he would order his MPs to vote against air strikes in Syria.
But he warned of "unintended consequences" if Britain got involved in military action in Syria in the same way it had in Iraq and Afghanistan.
Stressing there was "no doubt" IS had imposed a reign of terror in parts of Syria and Iraq and posed a threat to British people, Mr Corbyn said: "The question must now be whether extending the UK bombing from Iraq to Syria is likely to reduce or increase that threat, and whether it will counter or spread the terror campaign Isil is waging in the Middle East."
But his shadow foreign secretary Hilary Benn said there were "compelling arguments" for extending RAF air strikes from Iraq into Syria.
Mr Benn told the BBC: "I think our allies look to us - particularly the French, after the grievous blow they have suffered in Paris - and they want to feel we are with them in solidarity, and I think we should be."
The party's leader in the Lords, Baroness Smith of Basildon, said: "My party does not take an isolationist or non-interventionist position. We have never been reluctant to use force when it has been deemed necessary."
The shadow cabinet held a 90-minute meeting to discuss its position on Syria after the Prime Minister's statement, but no decision was reached on whether to back action or whip a vote.
A senior Labour source said "clarification" was needed on the exact form of the Commons motion and talks with the Government were likely to take place over the weekend.
In the Commons, Mr Cameron acknowledged IS - also known as Isis, Isil and Daesh - could not be defeated by air strikes alone, but stressed the need for action.
"The reason for acting is the very direct threat that Isil poses to our country and our way of life," he said.
"They have already taken the lives of British hostages and inspired the worst terrorist attack against British people since 7/7 on the beaches of Tunisia."
Mr Cameron - who flatly ruled out deploying British ground forces - said he was pursuing an "Isil-first" strategy while continuing to work for a long-term settlement for Syria.
"We do face a fundamental threat to our security. We can't wait for a political transition, we have to hit these terrorists in their heartlands right now and we must not shirk our responsibility for security or hand it to others," he said.
"Throughout our history the United Kingdom has stood up to defend our values and our way of life. We can, and we must, do so again."
Referring to the recent deadly attacks on Paris, the premier said: "If we won't act now, when our friend and ally France has been struck in this way, then our friends and allies can be forgiven for asking: If not now, when?"
During a sombre debate, several MPs - including the Tory chairman of the Defence Select Committee, Julian Lewis - questioned Mr Cameron's claim that there were 70,000 troops on the ground in Syria aligned to moderate groups.
Downing Street said that the figure had been provided by the Joint Intelligence Committee (JIC) - the UK's senior intelligence body.
Mr Cameron's hopes of a broad coalition were dealt a blow as the Scottish National Party's leader in Westminster Angus Robertson said that his party's MPs will not vote for air strikes in Syria unless they are convinced that there is effective ground support and a fully-costed plan for post-war reconstruction.
But Crispin Blunt, the chairman of the Commons Foreign Affairs Committee (FAC) - which earlier this month released a report urging caution over Syria - said he was now ready to back military action.
Mr Cameron set out his detailed case for extending air strikes to Syria in a 32-page response to the FAC, published shortly before his appearance in the Commons.
He said there was now "a realistic prospect" of a political solution to the four-year conflict and greater international consensus than ever before on the threat posed by IS.
Restricting UK air strikes to Iraq had "never made military sense", and the RAF - with Brimstone missiles and the Tornado aircraft's "dynamic targeting" capabilities - could make a "meaningful difference" to the campaign against IS, he said.