In the eyes of Mike Pompeo, the day was shaping up to be one of his most commanding displays of diplomacy since becoming secretary of state. Months of planning had finally yielded a meeting among reluctant European officials, Arab leaders and the Israeli prime minister to strategize over confronting Iran.

Iran’s top nuclear negotiator was heading back to Tehran on Sunday to consult with his nation’s leadership, as negotiators remained divided over how to limit and monitor Tehran’s nuclear program and even on how to interpret the preliminary agreement they reached two months ago.