GENEVA — Iran and six world powers remain split on terms of a nuclear deal because Tehran is resisting demands that it suspend work on a plutonium- producing reactor and downgrade its stockpile of higher-enriched uranium to a level that cannot quickly be turned into the core of an atomic bomb, France’s foreign minister said Saturday.

Laurent Fabius’ remarks to France-Inter radio were the first to provide some specifics on the obstacles at the Geneva talks, now in their third day. He spoke by telephone from Geneva, where he, U.S. Secretary of State John Kerry, Russian Foreign Minister Sergey Lavrov and counterparts from Britain and Germany negotiating with Iran consulted on how to resolve the obstacles at the talks.

Fabius mentioned differences over Iran’s Arak reactor southeast of Tehran, which could produce enough plutonium for several nuclear weapons a year once it goes online. He also said there was disagreement over efforts to limit Iran’s uranium enrichment to levels that would require substantial further enriching before they could be used as the fissile core of a nuclear weapon.

The six powers — the negotiators also include the EU and China — are considering a gradual rollback of sanctions that have crippled Iran’s economy. In exchange, they demand initial curbs on Iran’s nuclear program, including a cap on uranium enrichment to a level that cannot be turned quickly to weapons use.

Adding to the complexities at the negotiations were apparent divisions among the six powers on the shape of any deal.

A Western diplomat who is in Geneva for the talks said that most of the six powers were agreed on their demands but the French were holding out for tougher conditions on the Iranians. He gave no specifics and demanded anonymity because he was not authorized to comment on the diplomatic maneuvering among the six.