Negotiations over Iran's nuclear program reached a critical phase Monday with diplomats struggling to overcome substantial differences just a day before a deadline for the outline of an agreement.
With Tuesday's target date for a framework accord just hours away, the top diplomats from the five permanent members of the U.N. Security Council and Germany were meeting with Iran to try to bridge remaining gaps and hammer out an understanding that would serve as the basis for a final accord to be reached by the end of June.
"We are working late into the night and obviously into tomorrow," said U.S. Secretary of State John Kerry, who has been meeting with his Iranian counterpart Mohammad Javad Zarif in Lausanne since Thursday in an intense effort to reach a political understanding on terms that would curb Iran's nuclear activities in exchange for sanctions relief.
"There is a little more light there today, but there are still some tricky issues," Kerry said. "Everyone knows the meaning of tomorrow."
Kerry and others at the table said the sides have made some progress, with Iran considering demands for further cuts to its uranium enrichment program but pushing back on how long it must limit technology it could use to make atomic arms. In addition to sticking points on research and development, differences remain on the timing and scope of sanctions removal, the officials said.
German Foreign Minister Frank-Walter Steinmeier said Iran's expectations from the talks are "very ambitious" and not yet acceptable to his country or the other five negotiating: the U.S., Britain, China, France and Russia.
"We will not allow a bad deal," he said. "We will only arrive at a document that is ready to sign if it ... excludes Irangetting access to nuclear weapons. We have not yet cleared this up."
In particular, Steinmeier said the question of limits on research and development that Iran would be allowed to continue was problematic.
Other officials said the issue of the scope and timing of sanctions relief was also a major sticking point.
In a tweet, Gerard Araud, the French ambassador to the United States, said that "very substantial problems remain to be solved."
In a sign that the talks would go down to the wire on Tuesday, Russian Foreign Minister Sergey Lavrov left, just a day after arriving, to return to Moscow. His spokeswoman said he would will return to Lausanne on Tuesday only if there was a realistic chance for a deal.
Meanwhile, Iran's deputy foreign minister, Abbas Araghchi, told Iranian state television that the talks were not likely to reach any conclusion until "tomorrow or the day after tomorrow."
"We are not still in the position to be able to say we are close to resolving the (remaining) issues but we are hopeful and we'll continue the efforts," he said.
The Obama administration says any deal will stretch the time Iran needs to make a nuclear weapon from the present two to three months to at least a year. But critics object that it would keep Tehran's nuclear technology intact.
Israeli Prime Minister Benjamin Netanyahu, at the forefront of accusations that Iran helped Shiite rebels advance in Yemen, says the deal in the works sends the message that "there is a reward for Iran's aggression."
"But we do not shut our eyes, and we will continue to act against any threat," he said, an allusion to Israeli warnings that it will use force as a last resort against Tehran's nuclear program.
Officials in Lausanne said the sides were advancing on limits to aspects of Iran's program to enrich uranium, which can be used to make the core of a nuclear warhead.
Tehran has said it is willing to address concerns about its stockpiles of enriched uranium, although it has denied that will involve shipping it out of the country, as some Western officials have said.
Over the past weeks, Iran has moved from demanding that it be allowed to keep nearly 10,000 centrifuges enriching uranium, to agreeing to 6,000.
Tehran says it wants to enrich only for energy, science, industry and medicine. But many countries fear Iran could use the technology to make weapons-grade uranium.
Associated Press writer Aron Heller in Jerusalem contributed to this report.