Negotiators from Iran and the Group 5+1 (also known as the P5+1 or E3+3) launched a new round of talks in Lausanne, Switzerland, on Thursday with the aim of reaching a lasting nuclear agreement.
Iranian Foreign Minister Mohammad Javad Zarif and US Secretary of State John Kerry have been holding several bilateral meetings over the past days.
The parties have been working to agree on a preliminary framework accord by the end of March, to be followed by a comprehensive deal by June 30 that includes all technical details.
On Saturday, foreign ministers of France and Germany, Laurent Fabius and Frank Walter Steinmeier, arrived in Lausanne and held separate bilateral meetings with Zarif.
After those meetings, Zarif said he believed all sides could progress in such a way as "to resolve all the issues and start drafting a text that can be turned into a final deal."
The Russian, Chinese and British foreign ministers are also planned to arrive in the Swiss city on Sunday.
The European Union Foreign Policy Chief Federica Mogherini also joined the negotiations on Saturday.
Speaking to reporters in Lausanne, Mogherini, who coordinates diplomacy with Iran on behalf of the sextet, said the parties have never been closer to a deal.
"As you know, we have never been so close to a deal. We still have some critical points that need to be solved, and we are working over the hours, over the weekend to bridge the gaps," she noted.