Jeremy Corbyn has told ITV News that the Government should "look again" at the decision to target so-called Islamic State in Iraq.
"I'm not sure how successful it [military action in Iraq] has been because most of the action appears to have moved into Syria so I think we have to look again at that decision," the Labour leader told Chris Ship.
Mr Corbyn was speaking as Downing Street denied reports that Prime Minister David Cameron has abandoned hope of winning parliamentary approval to extend RAF operations into Syria.
Corbyn has previously called for a United Nations security council resolution and a fresh diplomatic push to end the violence in Syria saying the only solution would be a "political" one.
He said with Iran - a longtime supporter of Syrian president Bashir al-Assad - now involved in trying to devise a solution to the civil war, he hoped there would be progress soon.
"This underlines the need for a political settlement and a political solution to a desperate humanitarian crisis," he said.
"Two million refugees and rising, winter closing in, desperate people, desperate for food and support in all of the countries surrounding Syria - there needs to be further humanitarian aid but above all there has to be a political settlement.
"There seems to be some signs that that's improving, with the Vienna talks now including Iran. Iran should have been included from the beginning - maybe that's a way forward."