Islamic State is orchestrating terror plots against the UK from its Syrian stronghold, David Cameron will warn as he argues for an extension of British bombing raids into the group's heartland.
The Prime Minister will set out the case for RAF jets and drones to strike at targets in Syria, telling MPs that IS must not be allowed a "safe haven" in which to grow more dangerous.
He will say other nations should not be expected to "carry the burdens and the risks" of targeting IS in Syria "to stop terrorism here in Britain".
The Prime Minister has promised to set out a strategy for dealing with IS in his response to a report by the Commons Foreign Affairs Committee (FAC), which raised a series of concerns about the prospect of further UK military intervention.
"We need a comprehensive response which seeks to deal with the threat that Isil poses to us directly, not just through the measures we are taking at home, but by dealing with Isil on the ground in the territory that it controls," Mr Cameron will say.
The atrocities in Paris have strengthened his resolve on the issue and a vote on air strikes could take place as soon as next week, although Mr Cameron has insisted he will not "bounce" MPs into a decision.
The Prime Minister will only push his plans to a vote in the Commons if he is convinced there will be a clear majority in support, with aides fearful that a parliamentary defeat would hand a propaganda victory to the jihadis.
In a Commons statement he is expected to say: "Whether or not to use military force is one of the most significant decisions that any government takes. The need to do so most often arises because of a government's first duty: the responsibility to protect its citizens.
"Decisions to use force are not to be taken lightly. It is right that Parliament, on behalf of the people, asks difficult questions and holds the Government to account."
In his response to the FAC's report, expected to be published before the Commons statement, Mr Cameron will set out a seven-point strategy for Syria, including the need to use military force against IS, which is also known as Isil, Isis and Daesh.
"It is in Syria, in Raqqa, that Isil has its headquarters, and it is from Raqqa that some of the main threats against this country are planned and orchestrated," he will say. "We have to deny a safe haven for Isil in Syria.
"The longer Isil is allowed to grow in Syria, the greater the threat it will pose. It is wrong for the United Kingdom to sub-contract its security to other countries, and expect the aircrews of other nations to carry the burdens and the risks of striking Isilin Syria to stop terrorism here in Britain.
"That is why I believe that we should now take the decision to extend British airstrikes against Isil into Syria, as an integral part of our comprehensive strategy to degrade Isil and reduce the threat it poses to us."
The seven-point plan includes maintaining the UK's counter-terrorism capabilities, advancing a political settlement in Syria, delivering a credible government for the war-torn Middle East nation and defeating IS through "military and wider action".
The strategy will also involve continued humanitarian work, planning for the stabilisation and reconstruction of Syria and working with other nations to mitigate the impact of IS on the stability of the region.
The Government has argued that as well as the moral case for taking action against IS, the RAF can also offer a military capability lacked by other nations involved in the coalition with its high-precision Brimstone missiles.
Mr Cameron knows he will need the support of a significant number of Labour MPs to secure the clear majority he desires, but the Opposition's stance is unclear, with Jeremy Corbyn understood to have told colleagues that he wants to establish a collective position on the issue.
This could expose a deep rift, as while the leader has indicated he opposes military action against IS, a number of shadow ministers are likely to support it or choose to abstain.
The Prime Minister set out some of his thinking in the Commons on Wednesday when he told MPs that although airstrikes on their own would not be enough it would be wrong to wait for political progress in Syria before targeting IS.
He said: "One of the lessons I would say we should learn from the last century is that when your country is under threat, and when you face aggression against your country, you cannot endlessly sit around and dream about a perfect world—you need to act in the world we are in."
The massacre of civilians in Paris, progress in Syria peace talks in Vienna and a UN Security Council resolution calling on states to take "all necessary measures" to tackle IS have changed the position since the FAC's critical report.
The committee's Conservative chairman Crispin Blunt has indicated the conditions set in the report could now be met.