There is a moral and military case for British air strikes against Islamic State in Syria, Michael Fallon said as momentum continues to build towards a potential Commons vote on extending the scope of the RAF's mission.

The Defence Secretary said the Government is "building the case" for MPs to support action against the jihadist group in its Syrian stronghold, although David Cameron will not call a vote unless he is sure the Commons will back his push for a greater British role.

Mr Fallon said the rest of the international coalition against IS would like to see the RAF strike targets in Syria and there is "very little sense" in the UK attacking the terrorists in Iraq but not across the border.

The prospect of a Commons vote, potentially as early as next week, will depend on the ability of Mr Cameron to persuade Labour MPs to back him.

Although Jeremy Corbyn has called for renewed efforts to find a political solution in Syria rather than "external intervention", dozens of his MPs are ready to back strikes.

It appears increasingly likely they will be granted a free vote to avoid forcing possible frontbench resignations over the issue.

Shadow defence secretary Maria Eagle said it is even "conceivable" that Mr Corbyn himself could support strikes against IS - also known as Isil, Isis and Daesh - in Syria.

She told BBC Radio 4's Today programme: "My understanding is he is not a pacifist and that means that it is conceivable."

The process potentially leading to a vote will begin with the Prime Minister personally responding to a report by the Commons Foreign Affairs Committee in which he will make the case for action.

But Mr Fallon said the Government had not put a timetable on a vote on extending military strikes across the border from Iraq into Syria.

"It depends on MPs and us making our case to MPs," he said.

"There are a lot of new MPs and we have to make our case to them. Understandably they want to be sure that there is a political track to this as well, that we are working with everybody in the region to create a more comprehensive, moderate government in Syria that will bring long-term security after the striking has finished.

"But we will also be setting out the moral case - that we have now French aircraft, American aircraft, Australian aircraft coming half-way around the globe and we can't let them take all the burden, and indeed all the risk, of fighting Isil on our behalf."

Mr Fallon told Today: "We have a highly skilled air force. The Tornadoes that we have been deploying in Iraq have a high-precision missile, the Brimstone missile, that nobody else has, that reduces, eliminates, civilian casualties because it is so precise.

"The rest of the coalition would like to see the RAF engaged in Syria. It makes very little sense for the RAF to be able to fly as far as a border between Iraq and Syria that Isil itself does not recognise."

The Defence Secretary told ITV's Good Morning Britain that the Government would not risk a Commons defeat on intervention in Syria.

"There is no point having a vote and losing it. So we are going to keep building the case amongst Members of Parliament, particularly new Members of Parliament," said Mr Fallon.

"And if we get the right majority then we will strike in Syria. But we are going to go on with the campaign against Isil in Iraq."

Ms Eagle said a decision on whether Labour MPs would be whipped would not be taken until Mr Cameron came forward with his proposals.

"We will make decisions about the whipping arrangements, whether there is a whip, after we have made the decision about our policy on this and whether or not we are going to support it," she said.

She accepted the need to tackle IS, a "nihilistic death cult which is causing mayhem around Europe", but would not give consent for action without seeing the details of Mr Cameron's plan.

"If he satisfies us then there will be some support from the Labour Party for him to do what he wishes.

"But we are not there yet."