"I cannot say with certainty whether we will get a deal" by a July 20 deadline, German Foreign Minister Frank-Walter Steinmeier told reporters.
"It is now up to Iran to decide whether to take the path of cooperation with the international community. ... I hope that the days left until July 20 will be enough to create some reflection in Tehran," he said.
"The ball is Iran's court."
"We had a deep discussions but we have still not reached a deal," Fabius told reporters before leaving Vienna, describing the negotiations as "useful".
Also Read
Kerry was still in Vienna, however, and was due to hold talks later today with Iranian Foreign Minister Mohammad Javad Zarif.
The talks are aimed at securing a historic deal that would kill off once and for all worries that Iran -- which denies any such aim -- might develop nuclear weapons under the guise of its civilian programme.
The Islamic republic in return wants a lifting of all UN and Western sanctions that have crippled its economy, in particular its vital oil sector.
The July 20 deadline can in theory be extended but only if both sides agree and the United States in particular is opposed to such a move unless Tehran offers major concessions first.