VIENNA – Iranian construction of a previously secret uranium enrichment site is at an advanced stage, with high-tech equipment already in place at the fortified facility ahead of its 2011 startup, the International Atomic Energy Agency said in a report Monday.

The revelation of the existence of the underground plant known as Fordo, near the holy city of Qom, has heightened concerns of other possible undeclared Iranian facilities that are not subject to IAEA oversight and therefore could be used for military purposes.

In Washington, State Department spokesman Ian Kelly said the IAEA report "underscores that Iran still refuses to comply fully with its international nuclear obligations."

The IAEA report offered no estimate of Fordo's capabilities, but a senior international official familiar with the U.N. agency's work in Iran said it appeared designed to produce about a ton of enriched uranium a year.

The official, as well as analysts, said that would be enough for a nuclear warhead but too little for Iran's civilian reactors that have yet to come online, including the still unfinished plant at the southern port of Bushehr. The official spoke on condition of anonymity because the information he was citing was confidential.

"It won't (even) be able to produce a reactor's worth of fuel every 90 years, but it will be able to produce one bomb a year," said Ivan Oelrich, vice president of the Strategic Security Program of the Federation of American Scientists. "It does look strange."

The IAEA also said production at Iran's main enrichment site at Natanz — revealed by dissidents in 2002 and under IAEA monitoring — was stagnating at mid-2009 levels.

The report did not offer a reason. But the official suggested that experts who used to work at Natanz could be preoccupied with finishing the Fordo site.

As early as three years ago, Iran had said immediate plans for Natanz were to install about 8,000 enriching centrifuges, and Monday's report suggested Tehran had reached that goal.

The IAEA summary said that as of Nov. 2, about 8,600 centrifuges had been set up, but only about 4,000 were enriching — or 600 fewer than in September. Still, the official said output had been steady since June with about 220 pounds (100 kilograms) of enriched uranium being produced a month.

The report said Natanz had churned out nearly 4,000 pounds (1,800 kilograms) of uranium by Nov. 2 — close to what experts consider to be needed for two nuclear weapons. But for use as warhead material it would have to enriched further — it is now low-enriched uranium suitable only for fueling nuclear plants.

Iran insists it only wants to enrich uranium to make fuel to power nuclear reactors for civilian purposes, but fears that it could at some point use the technology to make weapons has resulted in three sets of U.N. Security Council sanctions meant to pressure Tehran into freezing the activity.

The restricted document, which was obtained by The Associated Press, also noted that "for well over a year," Iran had stonewalled IAEA efforts to investigate allegations it actively worked on a nuclear weapons program.

Unless Tehran has a change of heart, the IAEA "will not be in a position to provide credible assurances about the absence of undeclared nuclear material and activities."

The report's main focus was Fordo, a highly fortified underground space. Iran told the IAEA only in September that it was building the facility, leading U.S., British and French leaders to denounce Tehran for keeping it secret. IAEA inspectors visited the plant last month and the report noted "an advanced stage of construction," with support equipment, piping and electrical wiring for centrifuges already in place.

The report said the revelation of Fordo's existence "gives rise to questions about whether there were any other nuclear facilities in Iran which had not been declared" to IAEA.

The senior official said that as of Monday, Iran had failed to respond to a Nov. 6 IAEA letter asking for assurance Iran was not actively planning to build any other nuclear facilities.

But Iran says it fulfilled its legal obligations when it revealed the plant's construction, although IAEA chief Mohamed ElBaradei has said Tehran was "outside the law" and should have informed his agency when Iran decided to build it.

Nations suspicious of Iran believe it decided to tell the IAEA only after Tehran became convinced the plant's existence had been noted by foreign intelligence services and was about to be revealed by Western leaders.

A senior Western official recently told the AP that Fordo appeared too small to house a civilian nuclear program but large enough for military activities.

Monday's report — prepared for next week's meeting of the IAEA's 35-nation board — did not address the issue of size or function beyond saying the Fordo facility would house about 3,000 centrifuges, which the senior international official said could turn out about just over a ton of enriched uranium annually.

The report cited Iranian officials as suggesting Fordo was built covertly "as a result of the augmentation of threats of military attacks against Iran" — an allusion to past U.S. and Israeli suggestions that force could not be ruled out as a possible last resort to stop Tehran's nuclear defiance.

Reports Monday from Moscow cast more doubt on Iran's case that it needed to build up its nuclear fuel enrichment capacity through facilities such as Fordo and Natanz.

Officials in Russia and Iran had previously announced plans to turn on the Bushehr reactor, giving Iran its first operating nuclear power plant decades after construction began. But Russian Energy Minister Sergei Shmatko told Russian media that "the launch itself will not happen" in that time frame.

Shmatko blamed the delay on technical issues, the reports said. But Moscow has in the past has appeared to use the project to press Tehran to cooperate with international demands to freeze enrichment.

On Sunday, President Barack Obama pushed for continued pressure on Iran. In talks with Russian President Dmitry Medvedev in Singapore, Obama said "time is running out" for Iran to sign on to a deal with the IAEA.

Since September, Medvedev has suggested Russia could support further sanctions against Iran if it did not open its nuclear program to inspections to prove it was not trying to build a bomb. He spoke in similar terms Sunday, avoiding the word sanctions but saying "other options remain on the table" if Iran does not meet its obligations.

Shmatko said construction is proceeding as planned at Bushehr and that Russia "is certain that it will fulfill its commitments to Iran," according to RIA Novosti.

But his remarks raised hackles in Iran, already angry over Russian foot-dragging on fulfilling a 2007 contract to provide S-300 surface-to-air missiles to Tehran — also seen as a Russian lever in relations with Iran.

The semiofficial Mehr news agency quoted Alaeddin Boroujerdi, a parliamentary committee chairman, as saying "this hasty expression by (the) Russian energy minister does not look normal."

International frustration with Iran has intensified after Tehran first appeared to accept a plan meant to delay its ability to make a nuclear weapon, then backtracked.

Obama said Iran is running out of time to agree the plan to ship most of its low-enriched enriched uranium abroad to enrich it to a higher level. Diplomats told the AP that senior officials from the U.S., Russia, China, Britain, France and Germany, which are seeking to persuade Iran to accept an enrichment freeze, planned to meet this week to discuss a possible fourth round of U.N. Security Council Sanctions.

The West had hoped the plan on exporting Iran's enriched material would dramatically reduce its stockpile and delay its capacity to build nuclear weapons.

Iran is enriching uranium to less than 5 percent, enough to produce fuel but not for making arms. Enriching uranium to much higher levels can produce weapons-grade material.

Under a U.N. plan, after further enrichment in Russia, France would convert the uranium into fuel rods to be returned to Iran for use in a reactor that produces medical isotopes. Fuel rods cannot be readily turned into weapons-grade material.