More join Iran nuclear talks as negotiators race to meet looming deadline for deal

Negotiations over Iran's nuclear program picked up pace on Saturday with the foreign ministers of France and Germany joining U.S. Secretary of State John Kerry in talks with Iran's top diplomat ahead of a looming end-of-March deadline for a preliminary deal.

With just four days to go until that target, negotiators in the Swiss town of Lausanne settled in for another round of lengthy sessions that they hope will produce a two-to-three-page outline of an agreement that can then become the basis for a comprehensive deal to be reached by the end of June.

Beyond that document, key U.S. senators opposed to any deal as too lenient on Iran may be briefed in more detail by the Obama administration.

"We're expecting an evening today," Kerry told reporters when asked if he was expecting a good day at the start of his first meeting with Iranian Foreign Minister Mohammad Javad Zarif.

Kerry was to meet later with French Foreign Minister Laurent Fabius and his German counterpart Frank-Walter Steinmeier. The foreign ministers of Russia, China and Britain also are expected in Lausanne over the weekend.

Diplomats at the talks say, however, that their presence does not necessarily mean that a deal is almost done. They say some obstacles remain and the ministers are coming for consultations.

"The talks have been long and difficult. We've advanced on certain issues, not yet enough on others," Fabius told reporters as he arrived.

Iranian nuclear agency chief Ali Akbar Salehi described one or two issues as becoming "twisted," telling Iran's ISNA news agency that the sides were working to resolve the difficulties.

Iran says its nuclear ambitions are purely peaceful, but other nations fear it is seeking to develop weapons.

Progress has been made on the main issue — the future shape of Iran's uranium enrichment program, which can produce material for energy, science and medicine but also for the fissile core of a nuclear weapon. The sides have tentatively agreed that Iran would run no more than 6,000 centrifuges at its main enrichment site for at least 10 years, with slowly easing restrictions over the next five years on that program and others Tehran could use to make a bomb.

The fate of a fortified underground bunker previously used for uranium enrichment also appears closer to resolution. Officials have told The Associated Press that the U.S. may allow Iran to run hundreds of centrifuges at the Fordo bunker in exchange for limits on centrifuge work and research and development at other sites. The Iranians would not be allowed to do work that could lead to an atomic bomb and the site would be subject to international inspections.

Instead of uranium, any centrifuges permitted at Fordo would be fed elements used in medicine, industry or science, the officials said.

Even if converted to enrich uranium, the number of centrifuges would not be enough to produce the amount needed to make a weapon within a year — the minimum time-frame that Washington and its negotiating partners demand.

A nearly finished nuclear reactor would be re-engineered to produce much less plutonium than originally envisaged.

Still problematic is Iran's research and development program. Tehran would like fewer constraints on developing advanced centrifuges than the U.S. is willing to grant. Sanctions-lifting too, remains in dispute, with the Iranians wanting an up-front end to the economic restrictions — something the American are unwilling to do.

In addition, questions persist about how Iran's compliance with an agreement would be monitored.

In his comments, Fabius suggested that France was not yet satisfied on that point.

"Obviously, what's really important is the content of the commitments that are taken, but also — and I insist on this — the transparency of the mechanism and the control so that we are certain that the commitments made are respected," he said.