Working to meet a deadline of March 31, talks intent on inhibiting the nuclear program of Iran ended abruptly Friday, leaving both sides still split over several essential issues. Once word was received at the Lusanne, Switzerland talks that the mother of Iran’s President Hassan Rouhani was dead, it became clear that the delegation from Iran would take leave on Friday. One member of the delegation is Rouhani’s brother, Hossein Fereydoun, who departed for Tehran early in the day.

The March 31 deadline is for the completion of outline drafts of an agreement. Assuming that happens, a detailed agreement is planned for completion at the end of June.

Despite the interruption, United States officials said the talks would continue, likely restarting Thursday. Meanwhile, U.S. Secretary of State John Kerry is scheduled in London to meet with the some of his partners also negotiating in the talks, such as foreign ministers of Britain, Germany and France.

Mr. Kerry has at times described the talks as “tough” but said on Friday that some progress had been. Friday was Norwuz, the Persian New Year. In a statement he issued commemorating the event, Kerry called on Iran’s leadership to be flexible over the remaining differences.

Kerry said that if leaders from Iran “make the right choices” that “a better future” will be marked for the people of Iran “and for the world.” On the other hand, the foreign minister of Iran, Mohammad Javad Zarif, suggested via Twitter that the onus is now upon the U.S. and its partners to make make the allowances required to seal a deal.

One of the major items of contention has been about what specific sort of limitations will be established on research and development of uranium-enriching centrifuges in Iran. Also controversial has been disparities over – once an agreement is ratified – just how speedily sanctions that have been imposed by the United Nations Security Council, the European Union and the U.S. will be suspended or removed.