Jeremy Corbyn has called on the Government to re-think its bombing campaign against Islamic State extremists in Iraq.

The Labour leader said that RAF air strikes appeared to be having little impact on the militants, and called on ministers to "look again" at the strategy.

His comments came as Downing Street insisted David Cameron had not given up hope of winning a Commons vote to extend UK operations against IS - also known Isis, Isil or Daesh - into neighbouring Syria.

Mr Corbyn, who has consistently opposed military intervention in Iraq, told ITV News: "I'm not sure how successful it has been because most of the action appears to have moved into Syria, so I think we have to look again at that decision."

No 10 said that the UK action in Iraq had been backed by a majority of 481 MPs in a Commons vote last year.

"The Prime Minister is focused on what the Government can do to protect the British people from the threat of Isil. Action against Isil in Iraq is part of that," the Prime Minister's official spokeswoman said.

However, the suggestion by Mr Corbyn that Labour could try to force a rethink in Iraq is a further setback for the Government at a time when ministers are struggling to build a Commons consensus for action in Syria.

Number 10 denied reports that Mr Cameron had abandoned hope of winning parliamentary approval, but the prospect of an early vote appeared to be receding - with military action opposed not only by Mr Jeremy Corbyn but also by a group of 20-30 Tory MPs.

The Prime Minister's plans were dealt a further blow by a report from an influential Commons committee, which cautioned that he should not seek MPs' support until he could show there was a clear plan both to defeat the jihadists and end Syria's bloody civil war.

The strongly worded report by the Foreign Affairs Committee (FAC) warned that RAF strikes would only have a "marginal effect" and could compromise efforts to find a diplomatic solution to the crisis.

Chancellor George Osborne acknowledged there was currently no majority in the Commons for extending air strikes, but insisted the Government had not shelved plans for an eventual vote.

"Our position is very clear - we take the fight to Isis wherever we can," Mr Osborne told the BBC.

"But we are not going to go to the House of Commons unless we would be clear that we would win that vote and there would be a consensus for that action, and at the moment it's not clear that there is a majority for it.

"We continue to make the argument and when the time comes, we will put the vote to the House of Commons."

The FAC report acknowledged the "humanitarian and security catastrophe" in Syria meant there was a "powerful sense that something must be done", and that defeating IS was a "necessary goal for the UK".

But it added: "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."