A senior western diplomat cautioned on Thursday that any breakthrough in diplomacy over Iran's nuclear programme was not "close", seeking to dampen expectations the next round of talks on Nov. 7-8 could lead to a deal.
Western negotiators have described two days of nuclear talks with Iran in Geneva on Tuesday and Wednesday as the most detailed and serious to date after Tehran hinted it was ready to scale back sensitive atomic work to secure sanctions relief.
Despite the improved atmosphere, diplomats said major differences remained between western governments, which suspect Iran's nuclear work has covert military goals, and Tehran, which denies that and demands the lifting of crippling economic sanctions.
In Brussels, a senior diplomat said the talks in Geneva - the first such meeting since relative moderate President Hassan Rouhani took office in Iran in August - had left negotiators "more reassured than we were before".
"We learned more about their programme and their concerns," the diplomat said, speaking on condition of anonymity. "However, it doesn't mean we are close to a solution and that we will have an agreement next month."
In a series of meetings with Iran since last year, envoys from six world powers - the United States, Russia, China, France, Britain and Germany - have demanded that it abandon enrichment of uranium to 20 percent fissile purity, an important step on the way to producing weapons fuel, in return for modest sanctions relief.
Tehran has spurned their offer and demanded that major restrictions on trade in oil and on its banking sector are eliminated first.
Under Rouhani, Iran appears keen to push for a deal. Sanctions have drastically reduced the OPEC producer's oil export revenues and helped cut the value of its rial currency.
But Tehran remains in contravention of U.N. Security Council demands that it halt uranium enrichment and other sensitive nuclear activities.
Few details have emerged from the talks in Geneva this week, but in a sign of a dramatic shift from confrontation to dialogue, the two sides issued a joint statement to say that Tehran's proposals presented at the meeting were an "important contribution".
Nuclear experts and sanctions specialists from Iran and the six nations, led in diplomacy with Iran by the European Union's foreign policy chief Catherine Ashton, will meet in the coming weeks to prepare the next round of negotiations in Geneva.