Iran nuclear talks ended last week with enthusiastic pronouncements of progress from negotiators. Tehran's willingness to engage is a big step, but diplomats familiar with the meeting also say significant gaps remain between what the Iranians offered and what the six negotiating powers seek in order to reduce fears Iran wants to build nuclear weapons.

Details of the Iranian offer remain confidential, but two diplomats agreed to give The Associated Press some insight. They demanded anonymity because they are under orders not to discuss the issue.

The diplomats said the chief advance achieved at Geneva was not detailed Iranian concessions, but Tehran's apparent willingness to engage the six powers on their concerns — a departure from previous Iranian refusal to even discuss most of the other side's demands.

Differences remain over the size and output of Iran's enrichment program, which can create both reactor fuel and weapons-grade material suitable for a nuclear bomb.

Abbas Araghchi, Iran's deputy foreign minister, refused to confirm the characterization of negotiations, saying only that his country "introduced the framework for the talks" during the meeting and that they were welcomed. He said that Iran and the six powers had agreed to keep details confidential.

Iran, which denies any interest in such weapons, currently runs over 10,000 centrifuges that have created tons of fuel-grade material that can be further enriched to arm nuclear warheads. That's a relatively slow process with such reactor-grade material.

But Tehran also has nearly 200 kilograms of higher-enriched uranium in a form that can be turned into weapons much more quickly. Experts say 250 kilograms of 20 percent-enriched uranium are needed to produce a single warhead

The following is a list of demands on Iran from the six powers — the United States, Russia, China, Britain, France and Germany — and what the diplomats say Tehran offered at the Geneva talks:

Suspension of enrichment above reactor-fuel grade levels

— The six want Iran to stop enriching uranium to 20 percent. The diplomats say Iran offered to halt 20-percent enrichment at the Geneva talks, which ended Wednesday. They had already proposed this at the round preceding the Geneva talks.

Enrichment at Fordo

—The six demand that enrichment operations at Fordo, an underground bunker believed to be impervious to air strikes, be disabled to the point where they would be difficult to restart. The diplomats say Iran offered only to discuss the status of Fordo.

Limits on all uranium enrichment

— The six powers want a cap on how much enriched material Iran can produce and stockpile. With some of Iran's enriching centrifuges more efficient than others, this would mean tough negotiations on the number and type of machines it has installed and is operating. The diplomats say Iran has signaled it is open to discussing numbers.

Uranium stockpiles

—The six powers want Tehran to ship out most of its supply of 20-percent enriched uranium or blend it down into reactor fuel. They also want Iran to agree to stricter UN supervision of its lower-grade enriched uranium stockpile. The diplomats said the Iranians did not substantially address these demands.

Additionally, the diplomats said the Iranians agreed to discuss six power concerns about a reactor that experts say will produce enough plutonium for one or two bombs a year once completed. The U.S. and its allies have called on Tehran to stop construction of that reactor.

Araghchi predicted Monday the nuclear talks could take as long as a year in step-by-step measures with the first milestone coming in three to six months and negotiations concluding within the year.

Such as a timetable, however, could bring pressure on Washington from Israel and others that fear Iran could be seeking to buy time while making nuclear advances.

The diplomats said no formal implementation time table of any deal was discussed last week.

Experts from both sides are to meet at a yet unannounced date before the next round of talks in Geneva November 7-8. The diplomats said that only if that meeting makes progress in nailing down concrete issues to be negotiated at the Geneva talks can last week's round be called a success.