Top U.S. and Iranian diplomats returned to talks Tuesday, seeking to resolve differences blocking a deal that would curtail Iran's nuclear program and ease sanctions on the country. Among the issues they're now contending with is a Republican letter warning that any deal could collapse the day President Barack Obama leaves office.

Top U.S. and Iranian diplomats returned to talks Tuesday, seeking to resolve differences blocking a deal that would curtail Iran's nuclear program and ease sanctions on the country. Among the issues they're now contending with is a Republican letter warning that any deal could collapse the day President Barack Obama leaves office.

The letter,written by freshman Sen. Tom Cotton of Arkansas and signed by 46 other GOP senators,came up in talks Sunday between senior U.S. and Iranian negotiators, the official said, and the Iranians raised it again in negotiations Monday led by Kerry and Zarif.

Kerry and Zarif met for nearly five hours in the Swiss city of Lausanne Monday, before the Iranians departed forBrusselsfor talks with European negotiators.

There, EU foreign policy chief Federica Mogherini said "we are entering a crucial time, a crucial two weeks." German Foreign Minister Frank-Walter Steinmeier said after "more than 10 years of negotiations, we should seize this opportunity." British Foreign Secretary Philip Hammond said all sides were committed to trying. China, France and Russia are also involved in the negotiations.

In the end, European powers and Iran made little progress late Monday toward reaching an agreement to end the standoff over Tehran's nuclear program as an end-of-March deadline closes in.

The talks were aimed at narrowing gaps in the positions between Iran and the world powers, as part of a 15 month negotiating process that could see Iran freeze its nuclear program for at least a decade in exchange for the gradual lifting of international sanctions.

Iran says the program is aimed at generating electricity and at medical research, but many in the West fear the Islamic republic is trying to covertly build atomic weapons.

"It's always useful to talk but we, the French, want a solid deal," said French Foreign Minister Laurent Fabius. "Certain points are yet to be resolved, we hope we will be able to resolve them but as long as it's not done, it's not done."

Mogherini, who is negotiating with Iran on behalf of the world's five nuclear powers and Germany, said that all sides were aware how important it is to seal a good deal and that it was not clear whether "a technical solution" to fill the remaining gaps can be found.

"I see the elements for a deal to be reached but I still see the gaps that need to be filled," she said.

The world powers and Iran have set an end-of-March deadline to reach a framework accord on the way ahead. Some officials have said persistent differences mean negotiators could settle for an announcement that they've made enough progress to justify further talks.

Senior officials from the world powers will continue negotiations with Iran in Lausanne, Switzerland on Wednesday.

Iranian Foreign Minister Mohammad Javad Zarif, who represented Iran inBrussels, will also hold several days of discussions with U.S. Secretary of State John Kerry in Switzerland this week, as momentum builds in the nuclear negotiations.

Obama and other officials insist they're not going to make any deal that would allow Iran to acquire nuclear weapons. And the senior U.S. officialemphasisedthat in the end, the talks and a potential agreement depend on Iran showing the world that its nuclear program is exclusively peaceful. The goal for a full accord is the end of June.

The deal taking shape would limit Iran's uranium enrichment and other nuclear activity for at least a decade, with the restrictions slowly lifted over several years. Washington and other world powers also would gradually scale back sanctions that have crippled the Iranian economy. Tehran says it is only interested in peaceful energy generation and medical research, but much of the world suspects it harbors nuclear weapons ambitions.

http://www.neurope.eu/article/after-failure-brussels-iran-nuclear-talks-restart-lausanne