Major powers and Iran were pushing each other for concessions on Friday ahead of an end-March deadline for a preliminary nuclear deal, with Tehran demanding an immediate end to sanctions and freedom to continue sensitive atomic research, Reuters reported.
Tehran and six major powers -- the United States, Britain, France, Germany, Russia and China -- are meeting in Lausanne, Switzerland, to hammer out a political framework accord by the end of this month that would lay the foundations for a full deal by June 30.
Under a final settlement, Tehran would halt sensitive nuclear work for at least a decade and in exchange, international financial and oil sanctions on Iran would be lifted. This would aim to end Iran's 12-year nuclear standoff with the West and reduce the risk of war in the Middle East. While all sides agree they are moving closer to a deal, there are major disagreements.
Tehran insists on the freedom to continue research on advanced centrifuges, machines that purify uranium for use in nuclear power plants or, if very highly enriched, in weapons, at the underground Fordow site, and immediate lifting of all U.N. sanctions and the most severe U.S. and European Union sanctions.
"There has been massive progress on all the issues," a senior Iranian official told Reuters. "There are still disputes over two issues -- R&D (research and development) and U.N. sanctions."
A Western official close to the talks confirmed that centrifuge research and enrichment in general remained the most difficult unresolved issue.
The foreign minister of France, which negotiators say has demanded the most stringent limits on future Iranian nuclear activity if it is to support a deal, made clear there was more work to do while playing down the importance of the deadline.
"The important thing is the content not the deadline," Foreign Minister Laurent Fabius told reporters at the United Nations in New York. "There has been some progress, but there are things which are not yet solved."
Fabius is due to arrive in Lausanne on Saturday. His British and Russian counterparts have also confirmed that they will join the talks over the weekend. The Republican-led U.S. Congress has threatened to impose new U.S. sanctions on Iran if there is no March deal, against the advice of
President Barack Obama, who has threatened to veto any such moves.
The United States and European partners are reluctant to allow Iran to operate centrifuges at the Fordow site, Western officials said, adding that the issue was unresolved.
An Iranian government website said in November that Washington could let Iran keep some 6,000 early-generation centrifuges, down from nearly 10,000 now in operation.
After meeting U.S. Secretary of State John Kerry on Friday, Iranian Foreign Minister Mohammad Javad Zarif told reporters outside the 19th century hotel where the talks are taking place that it was unclear if there would be a deal in the coming days.
"We think an agreement is still possible but when is another story," Zarif said. "Our feeling is that we certainly will be able to reach an agreement, but that will need political will on the other side."
Zarif added that the issue of the Saudi-led military operations against Yemen's Houthi fighters, which Tehran has backed, had come up on the sidelines, though the Lausanne talks were exclusively focused on the nuclear issue.
Iranian President Hassan Rouhani spoke with his French, Russian, British and Chinese counterparts on Thursday in an attempt to break the impasse. He also sent a letter to the leaders of all six powers, including Obama, though officials said the letter did not suggest Tehran was ready to compromise.
When asked about French President Francois Hollande's conversation with Rouhani, Fabius said the Iranian president was "not very precise" regarding the nuclear negotiations but offered no details.
Western officials said the main problem remains Tehran's refusal to offer serious concessions. Iranian say the same thing about the six and accuse the French of taking the hardest line.
If there is a political framework agreement in the coming days, the U.S. and European delegations want it to be as specific as possible, including figures for permissible numbers of centrifuges Tehran could operate, uranium stockpiles and other sensitive technical issues.
Further technical details would be included in annexes to be agreed before July 1.
"We are not messing about here," a Western diplomat said. "If there is a deal it won't be a vague understanding that collapses as soon as we leave. If there is a political framework agreement, it will have the broad parameters of the issues."
The six powers want limits on the most sensitive aspects of Iran's nuclear program to be in place for at least a decade followed by years of intrusive U.N. inspections.
They also want to be certain Tehran would need at least one year to produce enough high enriched uranium for a weapon should the Iranians decide to produce one. Iran denies having any nuclear weapons ambitions.
Israel, Saudi Arabia, France and the U.S. Congress have all raised concerns that the Obama administration might be willing to conclude a deal that would allow Iran to develop a nuclear weapons capability in the future.