Iran and world powers will resume negotiations on its contested nuclear activities on July 2 after a round of talks in Vienna this week that Tehran said yielded no breakthrough on the main sticking points.
The six countries - the United States, Russia, China, France, Britain and Germany - and Iran are striving to reach a comprehensive deal by their self-imposed July 20 deadline in a bid to avert the risk of a new war in the Middle East.
But Iranian Foreign Minister Mohammad Javad Zarif said major differences persisted after five more days of talks in the Austrian capital, and urged the six nations to "abandon excessive demands which will not be accepted by Iran".
A senior Chinese official said the two sides had agreed on a "textual framework" in Vienna this week but gave no details.
"The fact that [we came up] with this text is progress...in procedural terms," a senior Chinese official, Wang Qun, told reporters after the talks.
Other diplomats told Reuters earlier in the week, however, that one of the most difficult issues in the talks, the number of centrifuges Tehran will be allowed to keep to enrich uranium under any deal, remained unresolved.
A spokesman for European Union foreign policy chief Catherine Ashton, who coordinates the talks, said only that the two sides had begun drafting the text of a deal at the talks in Vienna, their fifth round of negotiations so far this year.
"We have worked extremely hard all week to develop elements we can bring together when we meet for the next round in Vienna, beginning on July 2," Michael Mann said in a statement. "We presented each other with a number of ideas on a range of issues, and we have begun the drafting process."
The sides are seeking a settlement that would limit Iran's nuclear program, subject it to stricter U.N. inspections and lift sanctions impairing Iran's oil-based economy.
But with time running out if a risky extension of the talks past July 20 is to be averted, the two sides remain far apart over the permissible future scope of Iranian nuclear activity.
A diplomat with one of the six powers said on Thursday that some progress had been made in this week's round but "we have not concluded a big element of the negotiation".
"There are still a lot of differences between the two sides and they are important differences of substance."
The powers' overarching goal is to get Iran to scale back its uranium enrichment program, denying it any capability to move quickly into production of a nuclear bomb.
Iran denies any such ambition and demands crippling economic sanctions, eased slightly in recent months, be lifted swiftly as part of any settlement, something that Western governments are loath to do too soon, believing Iran will otherwise lose motivation to comply fully with terms of a final deal.
The sides also must resolve other complex issues, including the extent of U.N. nuclear watchdog monitoring of Iranian nuclear sites, how long any agreement should run and the future of Iran's planned Arak research reactor, a potential source of plutonium for atomic bombs.