France's foreign minister is joining talks on Iran's nuclear programme in Switzerland and has said he wants to achieve a "robust" deal.
Laurent Fabius joined US Secretary of State John Kerry and Iranian foreign minister Mohammad Javad Zarif ahead of a Tuesday deadline to agree a historic agreement that could see Iran scaling back its nuclear programme in exchange for sanctions relief.
"I am coming here with the desire to move towards a robust agreement," Fabius told reporters in Lausanne. "We have made progress on certain issues but not enough on others."
He said he was "insisting" that any deal included mechanisms to ensure that the Islamic republic complies with its commitments. 
German Foreign Minister Frank Walter Steinmeier was due to join his counterparts later on Saturday and hold a working lunch with Kerry and Fabius, US officials said. 
China and Russia's foreign ministers, the other two countries involved in the long-running talks, were reportedly expected on Sunday.

Al Jazeera's James Bays, reporting from Lausanne, said the negotiators had reached an "end phase" of the talks and were working hard to beat the deadline.
France has been tough and uncompromising at the negotiating table, reportedly demanding more stringent restrictions than other Western delegations. 
Six world powers - five of them permanent members of the UN Security Council plus Germany - have been involved in the negotiations seeking to agree a deal by March 31 that could pave the way for a broader and definitive agreement on how Tehran's nuclear programme should proceed. 
The West suspects Iran's nuclear programme is intended for military purposes although Tehran says it is meant to generate power.