The United States, Russia, Saudi Arabia and Turkey failed to resolve differences on the fate of Syrian President Bashar al-Assad in talks on Friday but could meet again in a week to discuss how to end Syria's civil war. Speaking to reporters afterwards, ministers said they had been unable to bridge the central dispute between Washington and its allies, who say Assad has no future in Syria, and Russia, which showed its support by hosting him in Moscow this week. In a separate development, Russia and Jordan agreed to coordinate their military actions on Syria by setting up a "special working mechanism" in the Jordanian capital, Amman, Russian Foreign Minister Sergei Lavrov said on Friday. Russia's three-week-old campaign of air strikes against Islamist groups opposed to Assad has halted an offensive by rebels, including some backed by the United States and its allies, which had eroded Assad's control in the west of Syria. Some diplomats and analysts believe Russia might be able to exploit its influence with Assad and its newly demonstrated military muscle in Syria's skies to broker a deal to end the conflict. Speaking after the roughly two-hour meeting, U.S. Secretary of State John Kerry acknowledged the fundamental disagreement but suggested that there may be a solution and spoke of the possibility of holding wider talks in a week's time. "I am convinced ... that today's meeting was constructive and productive and succeeded in surfacing some ideas, which I am not going to share today, but which I hope have a possibility of ultimately changing the dynamic," Kerry told reporters. "What we agreed to do today is to consult with all parties and aim to reconvene, hopefully as early as next Friday, with a broader meeting in order to explore whether there is sufficient common ground to advance a meaningful political process." He also pointedly did not exclude the possibility of bringing Iran, which backs Assad and is engaged in a regional power struggle with Saudi Arabia, into the discussions at some point. "Diplomacy has a way of working through very difficult issues that seem to be absolutely contradictory and, on their face, begin at odds. And this is one of those issues where the statements clearly - and current positions - are at odds," Kerry said, noting that Russia and Iran have argued that Assad's presence is vital to the stability of Syria. "But if we can get into a political process, then sometimes these things have a way of resolving themselves." Kerry would not be drawn on whether, or when, Iran might be drawn into the process. "We want to be inclusive and err on the side of inclusivity rather than exclusivity," he said. He added he was not opposed to the military agreement between Jordan, a close U.S. ally, and Russia. "We have no problem whatsoever with this effort and it may even help make certain that the targets are the targets that they ought to be." Strategy upended Russia's decision to enter the conflict with air strikes has upended the strategy of the United States and its regional and European allies. Washington is leading its own bombing campaign against Islamic State fighters who control swathes of eastern Syria and northern Iraq, so the Russian intervention means the Cold War-era superpower foes are now flying combat missions in the same air space for the first time since World War Two. Washington and Moscow both say they are targeting ISIS, but they have opposing visions of Syria's future, with Washington saying Assad must leave power to bring peace and Russia describing his government as a bulwark against militants. Russia describes all its bombing targets as belonging to ISIS. The United States and its allies say the overwhelming majority of Russian strikes have targeted other groups opposed to Assad, including groups they have backed. By tipping the balance of power on the battlefield in Assad's favour and making it less likely that his enemies will be able to drive him out, Moscow clearly hopes to improve his position in future talks. Winning a seat at the negotiating table for Assad's main backer Iran would be a major diplomatic victory. The U.S. position in the past has been that Tehran could play a part in Syrian diplomacy but only if it was prepared to act in a way Washington viewed as constructive. Iran, which has furnished advisers to aid Assad's forces on the ground and encouraged its Lebanese Shi'ite Hezbollah allies to fight on behalf of Damascus, repeated its position on Friday that Syrians must pick their leader - code for supporting Assad who has held elections which he overwhelmingly won. "Some parties who have so far backed terrorists in Syria, now should think about taking constructive steps," Iranian Deputy Foreign Minister Hossein Amirabdollahian said in remarks carried by IRNA news agency. He also expressed support for Russia's actions.