VIENNA – Iran expects to produce its first batch of higher enriched uranium in a few days but its initial effort is modest, using only a small amount of feedstock and a fraction of its capacities, according to a confidential document shared Wednesday with The Associated Press.

But the document also indicated that Iran was keeping silent on whether or not it would ramp up production, which would bring it closer to the ability to produce the fissile core of nuclear weapons.

The internal International Atomic Energy Agency document was significant in being the first glimpse at Iran’s plan to enrich uranium to 20 percent that did not rely on statements from Iranian officials.

Iran says it wants to enrich only up to that grade — substantially below the 90 percent plus level used in the fissile core of nuclear warheads — as a part of a plan to fuel its research reactor that provides medical isotopes to hundreds of thousands of Iranians undergoing cancer treatment.

But the West says Tehran is not capable of turning the material into the fuel rods needed by the reactor. Instead it fears that Iran wants to enrich the uranium to make nuclear weapons.

Iran denies such aspirations. But its move is viewed with concern internationally because it would create material that could then be processed into weapons-grade uranium more quickly and with less effort than Iran’s present stockpile of 3.5 percent enriched uranium.

On Wednesday, Iranian Vice President Ali Akhbar Salehi said the process of higher enrichment was going smoothly, a day after Iranian officials announced a start of the operation, but gave no details on the scope of the new activities. The restricted IAEA document, however, indicated that, for now at least, they were was modest in scale.

“It should be noted that there is currently only one cascade … that is capable of enriching” up to 20 percent, said the document. A cascade is 164 centrifuges hooked up in series that spin and re-spin uranium gas to the required enrichment level.

The document, relying on onsite reports from International Atomic Energy Agency inspectors, also cited Iranian experts at the enrichment plant at Natanz as saying that only about 10 kilograms — 22 pounds — of low enriched uranium had been fed into the cascade for further enrichment.

Agency inspectors were told Wednesday “that it was expected that the facility would begin to produce up to 20 percent enriched … (uranium) within a few days,” said the one-page document.

Iran has over 8,000 centrifuges at Natanz, although not all are working. It has amassed about 1.8 tons of low-enriched uranium — more than enough for one warhead should it opt for that choice.

Iranian officials have said that they expect to produce 3 to 5 kilograms (up to 12 pounds) of 20-percent uranium a month. David Albright of the Washington-based Institute for Science and International Security, said that at that rate, it would take Tehran about three years to produce enough for further enrichment into the 25 kilograms (55 pounds) of weapons-grade uranium needed for one warhead.

The IAEA document said the agency had asked for details on “the timetable for the production process (including the starting date and the expected duration of the campaign), along with other technical details.” Albright said that indicated that the Iranians were keeping silent on how long they would enrich to the higher grade and thus how much material they intended to produce.

“The IAEA is asking how much are you going to make, and they are not answering the question,” he said, adding that IAEA chief Yukiya Amano “has to assume the worst; that this is an open-ended campaign where more cascades are brought on line.”

Iran’s decision to enrich to higher levels has led to a spike in concerns about its nuclear arms — and led Washington on Wednesday to impose new sanctions on several affiliates of Iran’s Revolutionary Guard Corps over their alleged involvement in producing and spreading weapons of mass destruction.

The U.S. Treasury Department announced that it would freeze assets in U.S. jurisdictions of Revolutionary Guard Gen. Rostam Qasemi and four subsidiaries of a construction firm he commands, which was hit with U.S. sanctions in 2007.

The sanctions expand existing U.S. unilateral penalties against elements of the Guard Corps, which Western intelligence believes is spearheading Iran‘s nuclear and missile programs.

Western powers blame Iran for rejecting an internationally endorsed plan to export its enriched uranium, enrich the material further and return it in the form of fuel rods for the reactor — and in broader terms for turning down other overtures meant to diminish concerns about its nuclear agenda.

Iran, in turn, asserts it had no choice but to start enriching to higher levels because its suggested modifications to the plan were rejected.

That plan was welcomed internationally because it would have delayed Iran’s ability to make a nuclear weapon by shipping out about 70 percent of its low-enriched uranium stockpile. Tehran denies nuclear weapons ambitions, insisting it needs to enrich to create fuel for an envisioned nuclear reactor network.

The proposal was endorsed by the U.S., Russia, China, Britain, France and Germany — the six powers that originally elicited a tentative approval from Iran in landmark talks last fall. Since then, however, mixed messages from Tehran have infuriated the U.S. and its European allies, who claim Iran is only stalling for time as it attempts to build a nuclear weapon.

France and the U.S. have said Iran’s action left no choice but to push harder for a fourth set of U.N. Security Council sanctions to punish Iran’s nuclear defiance. China remains opposed, but Russia, which has close ties to Iran and has resisted new sanctions, appeared to edge closer to Washington’s position, with senior officials saying the new enrichment plans show the suspicions about Iran’s intentions are well-founded.

In an online briefing Wednesday, French Foreign Ministry spokesman Bernard Valero said that “we have no other choice today but to work with our partners to strengthen measures against Iran.” And Russian Deputy Foreign Minister Sergei Ryabkov told Interfax news agency that “working out a new sanctions resolution (now) takes on additional relevance.”

Still, he suggested Moscow was not in total sync with Western nations, saying they “are thrusting sanctions upon us.”

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Associated Press writers Ali Akhbar Dareini in Dubai, Veronika Oleksyn in Vienna, Matthew Lee in Washington, Jenny Barchfield in Paris, James Heinz in Moscow and Bradley S. Klapper in Geneva contributed to this report.