Abbas Araqchi, the Iranian deputy foreign minister, laid these divisions bare during an interview with state television. “For sure our research and development of advanced centrifuge machines should continue,” he said. “We insist on lifting of financial, oil and banking sanctions immediately.”
So far, these hurdles have been impossible to overcome. The negotiations with Iran are handled by the five permanent members of the Security Council – America, Britain, France, Russia and China – plus Germany.
Three of the “P5 plus 1” foreign ministers have left the talks: Sergei Lavrov of Russia, Wang Yi of China and Laurent Fabius of France. They are now represented by deputy ministers or officials.
Mr Steinmeier said that the “P5 plus 1” was prepared to consider new ideas from Iran at another late-night meeting, but he acknowledged the possibility that the talks might collapse.
Some progress has been made, notably over agreeing the size of Iran’s capacity to enrich uranium.
Philip Hammond, the Foreign Secretary, said that the contours of a possible agreement had been sketched out. “I think we have a broad framework of understanding, but there are still some key issues that have to be worked through,” he said.
“Some of them are quite detailed and technical so there is still quite a lot of work to do but we are on it now and we’ll keep going at it.”
If no deal is achieved, Mr Kerry would face an acute political problem. Now that his own deadline has been breached, the secretary of state may find it hard to dissuade Congress from undermining his diplomacy by imposing more sanctions on Iran.