WASHINGTON – Leaders from five world powers and Iran returned to the sight that witnessed a diplomatic breakthrough in 2015 on Iran’s nuclear work, hoping for another in light of US President Donald Trump’s May withdrawal from that landmark accord.But they emerged without any tangible progress, just weeks before the US is set to reimpose nuclear-related sanctions on Iran and those doing business with it.Tehran is threatening to withdraw from the deal unless Europe can guarantee it the economic benefits and protections that were built into the nuclear agreement.But returning US sanctions will target foreign businesses that continue to engage with Iran, and already, several EU corporations have pulled out of deals agreed to in the wake of the nuclear accord.Iranian Foreign Minister Javad Zarif claimed progress and said that the five world powers at the table – China, Russia, Britain, France and Germany – agreed that the US had isolated itself in withdrawing from the accord.But the Europeans expressed skepticism.Speaking after three hours of talks, EU foreign policy chief Federica Mogherini, who chaired the talks, read a statement from the six delegations repeating previously- announced broad priorities ranging from guaranteeing Iranian oil revenue to shipping ties, banking and all other trade and investment cooperation.“Participants agreed to keep progress under close review and to reconvene the joint commission, including at ministerial level, as appropriate in order to advance common efforts,” Mogherini said, adding that all sides were determined to find and implement solutions. Unlike at past meetings, Mogherini took no questions.“All the commitments made today should be implemented before the August deadline... it is up to the leadership in Tehran to decide whether Iran should remain in the deal... the proposal was not precise and a complete one,” Zarif told reporters.Speaking earlier in the day, France’s foreign minister said that world powers would struggle to keep to that deadline.“They must stop threatening to break their commitments to the nuclear deal,” Jean-Yves Le Drian said.“We are trying to do it [economic package] before sanctions are imposed at the start of August and then the next set of sanctions in November. For August it seems a bit short, but we are trying to do it by November,” he said.On Sunday, Iranian President Hassan Rouhani said he could see a path forward.“But to achieve that they need to take practical measures and certain decisions within the time limit,” he said. US sanctions will snap back in two parts, with a first round returning in August, and with the harshest sanctions returning in early November. The State Department is telling companies not to expect any waivers, claiming administration policy is to apply maximum economic pressure on the Iranian government.Reuters contributed to this report.