David Cameron should not ask MPs to back military action against Islamic State (IS) in Syria until he can show there is a clear plan to both defeat the jihadists and end the bloody civil war in the Middle East state, a powerful Commons committee has said.

In a major blow to the Prime Minister's hopes of extending the British mission against IS into Syria, the Foreign Affairs Select Committee said it was "not yet persuaded" that Mr Cameron would be able to address their concerns.

In a strongly-worded report, the Tory-led committee warned that RAF strikes would only have a "marginal effect", but could be a "distraction" and compromise efforts to find a diplomatic solution to the crisis.

The MPs acknowledged the "humanitarian and security catastrophe" in Syria meant there was a "powerful sense that something must be done", and that defeating IS - also known as Isil - was a "necessary goal for the UK".

But they said: "We believe that there should be no extension of British military action into Syria unless there is a coherent international strategy that has a realistic chance of defeating Isil and of ending the civil war in Syria.

"In the absence of such a strategy, taking action to meet the desire to do something is still incoherent.

"We consider that the focus on the extension of airstrikes against Isil in Syria is a distraction from the much bigger and more important task of finding a resolution to the conflict in Syria and thereby removing one of the main facilitators of Isil's rise."

The MPs said a bombing campaign would require "reliable" allies on the ground to identify targets and hold ground seized from IS, but the chaotic situation meant "these would not be easy to find".

Russia's intervention in the conflict "has complicated even further any proposed action in Syria by the UK", the report warned.

The committee set seven tests for the Government to pass before military action should be proposed, noting that they were "not yet persuaded" that Mr Cameron had the answers.

Committee chairman Crispin Blunt said: "We are concerned that the Government is focusing on extending airstrikes to Syria, responding to the powerful sense that something must be done to tackle Isil in Syria, without any expectation that its action will be militarily decisive, and without a coherent and long-term plan for defeating Isil and ending the civil war.

"There is now a miscellany of uncoordinated military engagements by an alarming range of international actors in Iraq and Syria, all of whom share an interest in defeating Isil and who between them possess an overwhelming capability to do so."

Committee member Stephen Gethins said: "I would urge the Prime Minister to consider this report and its findings very carefully."

Foreign Secretary Philip Hammond said: "Defeating Isil and ending the Syrian conflict are two faces of the same problem that Britain is working tirelessly with our international partners to overcome.

"Britain remains committed to using every tool available to save lives and create the conditions for peace in Iraq and Syria."