David Cameron warned against Syria vote by Commons committee
An influential Commons committee has urged David Cameron not to press ahead with a vote on UK air strikes against Islamic State militants in Syria.
The Foreign Affairs Committee - which has a Conservative majority - said the prime minister should instead focus on efforts to end Syria's civil war.
It also raised concerns about the legal basis for any UK action.
Downing Street has strongly denied reports Mr Cameron has abandoned plans for a vote altogether.
Chancellor George Osborne told the BBC the government's position had not changed and there was still an intention to ask MPs for authorisation for military action.
But Labour leader Jeremy Corbyn said there had to be a political solution and he did not believe that "more bombing is going to help in this".
A Downing Street source told the BBC the reports were "complete nonsense".
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The committee of MPs said no vote should take place on Syria until the government presents a "coherent international strategy" to defeat Islamic State (IS) and end the country's civil war.
It said it was "not yet persuaded" ministers could address its concerns.
A vote on extending RAF air strikes into Syria had widely been expected to take place in the autumn, although the prime minister had stressed he would only do so when he was sure of a "consensus" among MPs.
About 20-30 Conservative MPs were expected to rebel against their party in the event of a vote.
Mr Cameron was defeated in a 2013 vote on possible UK military action against Syrian President Bashar al-Assad's government by 285-272.
Following that vote, he said he would respect the decision, and ruled out joining US-led strikes - although it later emerged that UK pilots embedded with coalition forces had conducted air strikes against IS over Syria.
BBC political correspondent Ross Hawkins said it was widely acknowledged that Russia's bombing campaign in Syria and deep splits within Labour made any swift attempt to seek the consent of MPs for air strikes unlikely.
Russia began those attacks in September, with President Vladimir Putin saying the aim was to "stabilise the legitimate authority" of President Assad.
A Downing Street source said: "The prime minister's position hasn't changed. He's consistently said that we would only go back to the House on this issue if there was clear consensus and that remains the case."
The government is "working closely with our allies to inject greater momentum into efforts to find a political solution", the source added.
However, some Conservatives told the BBC they were concerned by the newspaper reports.
One senior party figure said if the prime minister had decided not to seek military action, then ministers should come to the House of Commons to explain their position.
Mr Osborne said the government would not return to the Commons for authorisation "unless we would be clear we would win that vote, and there would be consensus for that action".
He added: "And at the moment it's not clear there is a majority for it, so as I say we continue to make that argument and when the time comes we'll put the vote to the people in the House of Commons."
Meanwhile, the Foreign Affairs Committee warned that any benefits of air strikes in Syria would be more than outweighed by the risks of "legal ambiguity, political chaos on the ground, military irrelevance, and diplomatic costs".
- While intervention would be welcomed by the UK's military allies, it would be likely to have only a "marginal effect" on the conflict
- The UK risks "further reputational" damage unless it can make a clear legal case for action, with a UN mandate the clearest basis
- It is "hard to predict" the consequences of tackling IS alone, and who might take their territory if they are defeated
- Russia's recent intervention has "complicated even further" any proposed UK action
The committee said there was a "powerful sense that something must be done" given the "humanitarian and security catastrophe" in Syria, and agreed that defeating IS, also known as Isil, was a "necessary goal" for the UK.
It added: "However, 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."
The committee outlined a series of points that should be explained before the government asks MPs to back its case.
These include how the action would improve the chances of success against IS, how it would contribute to a transition plan for Syria, and whether the UK has the backing of "key regional players" Turkey, Iran, Saudi Arabia and Iraq.
The MPs also want to know which ground forces would take control of land captured from IS.
They said the government was attempting to treat IS and the broader Syrian civil war as separate issues, saying they were "not persuaded" by such an approach.
Committee chairman Crispin Blunt said: "By becoming a full combatant in the US-led campaign at this stage, the UK risks needlessly compromising its independent diplomatic ability to support an international political solution to the crisis."
Labour leader Mr Corbyn is opposed to military intervention, although not all of his MPs share this stance.
On Monday night, shadow foreign minister Catherine West said Labour would consult the Stop the War Coalition ahead of any vote, BBC political correspondent Ross Hawkins reported.
Stop the War is opposed to any military action and believes the United States is to blame for the lack of a ceasefire in Syria.
Mr Corbyn stepped down as the coalition's chairman after becoming Labour leader but continues to support its work.
Ms West later said her comments, at a Stop the War event at Westminster, had been addressed to a group of Syrian refugees at the meeting, but a Labour spokesman confirmed the party would "listen to representations from the Stop the War Coalition, as it would from other external bodies, before coming to any decision".
Shadow foreign secretary Hilary Benn has not ruled out supporting air strikes and Labour MPs could have been offered a free vote, meaning they would not have been bound by the party line.
But Mr Benn told Sky News there wasn't a government "proposition" on the table at the moment, claiming it had taken its "eye of the ball" and focused on military action at the expense of "comprehensive" efforts to build diplomatic support in the region and deal with the refugee fallout.
Foreign Secretary Philip Hammond said defeating IS and ending the Syrian war were "two faces of the same problem that Britain is working tirelessly with our international partners to overcome".
He added: "Britain remains committed to using every tool available to save lives and create the conditions for peace in Iraq and Syria."