GENEVA -- With only weeks left before the deadline to reach a first-stage nuclear deal with Iran, U.S. Secretary of State John Kerry said Saturday that "significant gaps" remained and warned that Washington is ready to walk away from the talks if Tehran doesn't agree to terms demonstrating that it doesn't want atomic arms.
Kerry spoke after Iranian Atomic Energy chief Ali Akbar Salehi and U.S. Energy Secretary Ernest Moniz joined the talks for the first time to help resolve technical disputes standing in the way of an agreement meant to curb Iran's nuclear programs in exchange for sanctions relief for the Islamic Republic.
Both men researched nuclear physics at the Massachusetts Institute of Technology during the 1970s.
The scientists are participating in the talks "so technical issues can be solved at the highest level," an Iranian government website said via Twitter.
But Kerry warned against undue optimism. Salehi's and Moniz's presence is no "indication whatsoever that something is about to be decided," he said. "There are still significant gaps."
World powers and Iran have set an end-of-March deadline for a framework agreement, with four more months for the technical work to be ironed out. The talks have missed two previous deadlines, and President Barack Obama has said a further extension would make little sense without a basis for continuing discussions.
Kerry, who flies to Geneva today from London, said there was no doubt Obama was serious. The president, he said, "is fully prepared to stop these talks if he feels that they're not being met with the kind of productive decision-making necessary to prove that a program is in fact peaceful."
If the talks fail, Obama may be unable to continue holding off Congress from passing new sanctions against Iran. That, in turn, could scuttle any further diplomatic solution to U.S.-led attempts to increase the time Tehran would need to be able to make nuclear arms. Iran denies any interest in such weapons.
Skepticism about the negotiations already is strong among congressional hard-liners, Washington's closest Arab allies and Israeli Prime Minister Benjamin Netanyahu, who is expected to strongly criticize them in an address before the U.S. Congress early next month.
Western officials say the U.S. decided to send Moniz only after Iran announced that Salehi was going.
Salehi received his doctorate in nuclear engineering from MIT in 1977. In his research thesis, written about the way neutrons move in different reactors, Salehi thanked the U.S. Atomic Energy Commission for partly funding his studies.
Four years earlier, in 1973, Moniz was appointed to MIT's faculty. He published four papers the year Salehi graduated on topics including electrodynamics and nuclear physics, MIT records show.
MIT received about $1 million from the Iranian government to train 23 students in the 1970s, according to online records published by Harvard University.
The men were expected to discuss the number of centrifuges Iran can operate to enrich uranium, how much enriched material it can stockpile, what research and development it may pursue related to enrichment, and the future of a planned heavy water reactor that could produce substantial amounts of plutonium -- which like enriched uranium is a potential pathway to nuclear arms.
Since signing a 2013 interim accord that saw Iran suspend its most sensitive nuclear activities in exchange for limited sanctions relief, the sides have remained at loggerheads. The arrival of Moniz and Salehi may mean the sides are ready to compromise, according to International Crisis Group analyst Ali Vaez.
"The presence of Salehi and his American counterpart shows that technical discussions are nearing their end," Vaez said in an email.
Iranian Foreign Minister Mohammad Javad Zarif is also at the talks, and Kerry is to meet him today and Monday.
For months, the negotiations have been primarily between Washington and Tehran. But Kerry insisted "there is absolutely no divergence" between the U.S. and the five other powers -- Russia, China, Britain, France and Germany -- over what Iran needed to agree to, "to prove that its nuclear program is going to be peaceful in the future."
Information for this article was contributed by George Jahn and Bradley Klapper of The Associated Press and by Jonathan Tirone of Bloomberg News.
A Section on 02/22/2015