Iran said Tuesday it was not prepared to ship most of its enriched stockpile out of the country, effectively rejecting a plan designed to delay its ability to build a nuclear weapon. Diplomats said six world powers were preparing to criticize Iran's nuclear defiance at a meeting later this week.

While saying it was ready to exchange its low-enriched uranium with a higher enriched material, and Iranian official said Tehran would do so only on home soil to guarantee the West follows through with promises to give the fuel.

Foreign Ministry spokesman Ramin Mehmanparast said Iran had sent its response on the proposal to the five permanent members of the U.N. Security Council plus Germany, saying it wants a simultaneous exchange on Iranian soil.

"Iran's answer is given. I think the other side has received it," said Mehmanparast. "The creation of a 100 percent guarantee for delivery of the fuel is important for Iran."

Iranian officials have accused the West of breaking past promises to supply it technology. They say they don't trust that the West will eventually send back the fuel rods if Iran lets its uranium abroad.

The United States and its European allies accuse Iran of embarking on a nuclear weapons program. Iran denies the claim, saying its program aims only to generate electricity.

Low enriched uranium is used to fuel a nuclear energy reactor, but highly enriched uranium can be turned into a warhead. The plan, brokered by International Atomic Energy Agency chief Mohamed ElBaradei aims to ensure that Iran, at least temporarily, does not have enough low enriched fuel that it could process further to build a bomb.

Under the plan, Russia and France would enrich Iran's uranium to a medium level of 20 percent and produce fuel rods for Iran's research reactor, which is used for medical purposes. The rods cannot be readily turned into weapons-grade material.

In Vienna, the six-power move to criticize Iran in the form of a draft resolution for an upcoming International Atomic Energy Agency board meeting reflected international exasperation with the country's nuclear defiance.

The diplomats told The Associated Press that the draft document calls on Iran to be more open about its nuclear plans following its recent revelation that it had secretly nearly completed building a new uranium enrichment facility.

The draft urges Iran to throw open its nuclear program to wider perusal by the IAEA, they said. As well, it calls on Iran to answer all outstanding questions on that enrichment facility, comply with U.N. Security Council demands that it suspend enrichment as well as further construction of the plant, and stop stonewalling an IAEA probe of allegations it tried to develop nuclear weapons.

The development is significant because it groups Russia and China with the four Western powers — the U.S., Britain, France and Germany — in unified criticism of Iran's nuclear program. Russia and China have acted as a drag on Western calls for tougher action against Iran.

While the board passed an IAEA resolution critical of Iran in 2006 that had the support of all six world powers, subsequent attempts by the West to get backing from all 35 board nations foundered on resistance from Russia and China.

Those two nations have also resisted U.S. and European calls for tougher U.N. sanctions against Iran for refusing to freeze its enrichment program.

While any board resolution is mostly symbolic, it does get reported to the Security Council. Beyond that, unified action in Vienna could signal that both Russia and China may be more amenable to a fourth set of Security Council sanctions on Iran over its nuclear program than they have been in past years.

The diplomats spoke two days before the board meeting. They demanded anonymity because their information was confidential.

Since its clandestine enrichment program was revealed in 2002, Iran has continued to expand that activity, asserting it needed it to make nuclear fuel for a future network of reactors. But concerns about enrichment's other use — creating fissile nuclear warhead material — has led to steady international pressure on the Islamic Republic to freeze enrichment — something Iran refuses to do.

The six-power move appeared to reflect disenchantment with Iran's latest refusal to diminish fears about its nuclear aims, with Iran refusing the enrichment export offer.

Iran initially agreed in principle to the offer from the six nations. The plan would have delayed any Iranian ability to create warhead material by stripping it of most of its enriched stockpile.

Iran has accumulated enough low-enriched material for up to two nuclear weapons, should it decide to further enrich to weapons-grade.