Russia voiced skepticism Tuesday about Iran's announcement of a dramatic expansion of its uranium enrichment effort, saying it had not received independent confirmation of the claim.

Iran said Monday it has begun operating 3,000 centrifuges — nearly 10 times the previously known number — in defiance of U.N. demands that it halt its nuclear program or face increased sanctions.

Russia was unaware, however, of "any recent technological breakthroughs in the Iranian nuclear program that would change the format of its enrichment effort," Foreign Ministry spokesman Mikhail Kamynin said in a statement.

"We haven't got a confirmation yet that they have actually begun uranium enrichment at the new cascades," of centrifuges, Foreign Minister Sergey Lavrov told reporters.

In the enrichment process, uranium gas is pumped into centrifuges, which spin and purify the gas. Enriched to a low degree, the result is fuel for a reactor, but to a high degree it creates material for a nuclear warhead.

The United States and its allies accuse Iran of seeking to develop nuclear weapons, a charge Tehran denies.

U.S. experts say 3,000 centrifuges are, in theory, enough to produce a nuclear weapon, perhaps within a year. But they doubted Iran had so many operational, a difficult technical feat given the country's patchy success with a much smaller number.

Iran's President Mahmoud Ahmadinejad claimed Monday that his nation had "joined the nuclear club of nations and can produce nuclear fuel on an industrial scale" — comments suggesting Iran was able to produce enough enriched uranium to fuel a nuclear reactor consistently. Vice President Gholamreza Aghazadeh said that Iran would install 50,000 centrifuges.

"We have heard the Iranian president's statement and have adopted a serious attitude to what is going on in relation to the Iranian nuclear program," Lavrov said Tuesday. "But we would like to proceed from facts, not from emotional political gestures."

Kamynin on Tuesday urged Tehran to cooperate with the U.N. nuclear watchdog and voiced concern about the latest Iranian statements.

Russia has developed close economic ties with Iran and is building its first nuclear power plant in the southern port of Bushehr.

Russia, however, has delayed Bushehr's launch that had been earlier set for September and refused to ship uranium fuel for the reactor last month as earlier planned, citing Iran's payment arrears. Iranian officials denied any payment delays and accused Russia of caving in to Western pressure.

Russia and China joined the rest of the U.N. Security Council last month in voting to impose the new sanctions — the second in three months against Iran for its refusal to suspend uranium enrichment.

The sanctions included the banning of Iranian arms exports and the freezing of assets of 28 people and organizations involved in Iran's nuclear and missile programs.

Iran rejected the sanctions and announced a partial suspension of cooperation with the International Atomic Energy Agency.