"We held very useful talks with the six nations and made certain progress, greater than before. Our work continues. There are still differences that we need to overcome, but we are working hard on it," Abbas Araghchi told journalists.
Araghchi also stated that better understanding on a number of difficult problems was reached, however, unsolved issues still remain.
Iran and the P5+1 group of international mediators, comprising the United States, Russia, China, the United Kingdom, France and Germany, have held several rounds of talks in the Swiss resort of Montreux in March. The negotiations were preceded by a series of bilateral meetings aimed at reaching a nuclear deal meant to curb Tehran's controversial nuclear program.
The P5+1 has been negotiating a long-term nuclear deal with Iran since November, 2013. By the end of March, the parties are expected to work out the outline of the deal. The deadline for reaching a final agreement has been set for July, 2015.