VIENNA (AP) -- Iran is moving ahead to update a program the West fears could be used to make nuclear weapons, diplomats said Wednesday, despite high-level diplomacy aimed at stopping it from doing so.

Three diplomats said Tehran now has installed close to 700 high-tech centrifuges in an upgrade of its uranium enrichment program since the start of the year. That represents an increase of about 100 since mid-April, when diplomats first told The Associated Press that Iran was rapidly installing the equipment.

Tehran says it is enriching uranium only for peaceful uses. But the U.S. and its allies fear it may enrich to levels used for nuclear bombs. The Islamic Republic is under U.N. Security Council and other sanctions for refusing to stop enrichment and the International Atomic Energy Agency is attempting to probe suspicions it may have worked on nuclear weapons.

But other countries say there is no proof that Iran intends to use the technology for weapons, and they support Iran's claim that Security Council sanctions because of its refusal to stop enriching are illegal.

The International Atomic Energy Agency is expected to report on the centrifuge installations Wednesday. The diplomats, all from IAEA member nations, demanded anonymity because they are not authorized to divulge confidential IAEA information. Two are from countries critical of Tehran's nuclear program while the third is considered neutral.

The new IR-2m centrifuges are believed to be able to enrich two to five times faster than the old machines. For nations fearing that Iran may want to make nuclear arms, that would mean a quicker way of getting there.

Ali Asghar Soltanieh, Iran's chief IAEA representative, said he would not comment ahead of the IAEA report. IAEA spokeswoman Gill Tudor said the agency would not comment.

The IAEA first reported initial installations in February. It said then that agency inspectors counted 180 of the advanced IR-2m centrifuges at Natanz, Tehran's main enrichment site, less than a month after Iran's Jan. 23 announcement that it would start installing them.

The diplomats said none of the machines appeared to be operating and some may only be partially set up. But the rapid pace of installations indicates that Iran possesses the technology and materials to mass-produce centrifuges that can enrich much faster than its present machines.

Iranian nuclear chief Fereidoun Abbasi said earlier this year that more than 3,000 high-tech centrifuges have already been produced and will soon phase out the more than 12,000 older-generation enriching machines at Natanz, south of Tehran. The IAEA report also is expected to mention that Tehran has put in hundreds more of those old machines even as it expands its upgrade with new centrifuges.

The diplomats said the agency will also note Iran's decision to keep its stockpile of uranium enriched to a level just a technical step away from weapons-grade to below the amount needed for a bomb.

Two of the diplomats also said that Iran has begun converting a small reactor to test fuel for a bigger reactor now being built that the U.S. and its allies say will yield enough plutonium for several bombs a year.

The large reactor is being built at Arak, southwest of Tehran, while the tests are being planned at the nuclear research facility at Isfahan, in central Iran. Tehran says the Arak facility will go on line early next year, but experts say the earliest they expect that to happen is 2015.

Iran says the Arak reactor will be used only for research and other peaceful purposes, adding it has no intention of reprocessing plutonium for weapons use.

More than six years of international negotiations have failed to persuade Tehran to stop enrichment and mothball the Arak reactor.