Iran and major powers gave themselves until Monday to reach a nuclear agreement, their third extension in two weeks, as Tehran accused the West of throwing up new stumbling blocks to a deal.
Both sides say there has been progress in two weeks of talks, but British Secretary Philip Hammond called it "painfully slow" and he and his French counterpart, Laurent Fabius, left Vienna saying they would return on Saturday.
Having missed a Friday morning U.S. congressional deadline, U.S. and European Union officials said they were extending sanctions relief for Iran under an interim deal through Monday to provide more time for talks on a final deal.