Secretary of State John Kerry is staying at Iran nuclear talks, and so is Iranian Foreign Minister Mohammad Javad Zarif. But foreign ministers of the five other nations at the negotiating table are leaving or have already left, reflecting a rough slog ahead for a deal.

All seven ministers had arrived to Vienna over the past few days in hopes their added diplomatic weight would clinch agreement. But they decided to leave after talks busted through a second extension on Tuesday, with Russian Foreign Minister Sergey Lavrov saying the sides were still apart over nearly 10 issues.

The new tentative target date for a deal now is Friday. The U.S., backed by Russia, China, Britain, France and Germany, want long-term curbs on Iran's nuclear program, offering Tehran sanctions relief in return.