The American push to quickly begin high-stakes talks with Iran hit a snag Friday, just days after the signing of an agreement that opens a two-month window for negotiations on Tehran's nuclear program and returning oil traffic through the Strait of Hormuz to prewar levels.

Iranian officials did not travel as planned to Switzerland, insisting that Israel strikes on Iranian-backed Hezbollah militants Lebanon must stop before the talks can take place, according to three regional officials and a person familiar with the matter. They were not authorized to publicly discuss the ongoing mediation to try to get the talks rescheduled and spoke on condition of anonymity.