Moscow regrets Tehran's decision to enrich uranium near the city of Qom, Itar-Tass state-run news agency quoted a foreign ministry official as saying on Tuesday.

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"Moscow has met reports on the start of uranium enrichment at an Iranian plant near Qom with regret and concern," the agency quoted a Foreign Ministry official as saying.

"We should recognize that Iran is continuing to ignore the demands of the international community that it respond to their concerns regarding its nuclear program," the official was quoted as saying.

“Hopefully, Iran will listen to our opinion about the need for further close cooperation with the Agency and the soonest beginning of serious negotiations on the Iranian nuclear program with the Sextet without preconditions,” the Russian Foreign Ministry said.

The International Atomic Energy Agency, the UN nuclear watchdog, confirmed on Monday that Iran has started enriching uranium up to 20 percent at an underground site at Fordo, near the Shi'ite Muslim holy city of Qom, and said all atomic material there was under its surveillance.

The United States said on Monday that if Iran is enriching uranium to 20 percent at an underground facility at Fordo, this would be a "further escalation" of its pattern of violating its obligations under UN Security Council resolutions.

"The fact that the IAEA has made clear that they are enriching to a level that is inappropriate at Fordow is obviously a problem," a State Department spokeswoman told reporters.

Nuland said the Vienna-based IAEA's assessment, previously reported by diplomats in Vienna, did not come as a surprise to the U.S.

"If they are enriching at Fordow to 20 percent, this is a further escalation of their ongoing violations with regard to their nuclear obligations," Nuland said, referring to a series of UN Security Council resolutions calling on Iran to halt its enrichment-related activities.

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