The sanctions have contributed to Iran's acute economic struggles.

The European Union's foreign policy chief, Catherine Ashton, said the six nations were forced to make concessions since the last talks in Moscow last year in May.

"We put what we call a confidence-building proposal on the table," Ashton said in a statement. "This is an opportunity for Iran to take some initial steps that would improve the confidence of the international community in the wholly peaceful nature of their nuclear program, in return for which we would do some things as well."

The two sides are to meet next in Istanbul on March 18 for talks involving technical experts.