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Iran refused to back down Wednesday in crucial talks on Russia's offer to enrich uranium for Tehran, but negotiators agreed to resume discussions Thursday on a plan meant to ease Western fears Iran wants to build an atomic bomb.

The chief Iranian nuclear negotiator also said his country did not intend to agree to Russian demands to impose another moratorium on uranium enrichment activity.

"I want to say that the process of enrichment is the sovereign right of any country," Ali Larijani said after nearly five hours of talks in a Moscow hotel. "You should not take away this right from nations which have a peaceful nuclear program, which consequently, includes also enrichment."

That drew an immediate response from the United States, which fears Iran will use enrichment to make uranium for a weapons program. Deputy State Department spokesman Adam Ereli said Larijani's declaration was "a move in the wrong direction" and cause for concern.

Iran's decision was "one of the reasons why, after trying to resolve this issue through negotiations and through a good and reasonable proposal from Russia, we're having to go to the (U.N.) Security Council," Ereli said.

Russia, whose offer to host Iran's uranium enrichment program has been backed by the United States and the European Union, acknowledged the talks were deadlocked. The enrichment offer is seen as a way to provide more assurances that Tehran could not divert uranium for military purposes.

"There was a constructive and serious discussion, but many questions remain unresolved," Russian Deputy Foreign Minister Sergei Kislyak was quoted as saying by the Interfax news agency.

However, with pressure mounting to move toward sanctions against Iran when the U.N nuclear watchdog's board of governors meets Monday, a joint statement said efforts to resolve the nuclear dispute should remain within the framework of the International Atomic Energy Agency.

"Both sides underlined the importance of talks and consultations for the resolution of the nuclear problem through diplomatic means and within the framework of the IAEA," said the statement issued by Russia's Security Council.

Iran insists its nuclear program is only to generate power, but many in the West — particularly the United States — fear Iran is aiming to develop atomic weapons. Enrichment is a process that can produce fuel for a nuclear reactor or fissile material for a weapon.

Larijani said that talks would resume Thursday ahead of the Iranian delegation's departure that day, according to RIA Novosti.

However, Kseniya Roshchina, a Russian spokeswoman, said she could not confirm whether further discussions would take place Thursday.

Wednesday's meeting marked a third round of talks after two previous negotiating sessions last week that made no visible progress. Igor Ivanov, the secretary of the Russian Security Council, led the Russian delegation.

Russia's top diplomat reiterated Moscow's call for Iran to return to a moratorium on enriching uranium as a condition for going forward with the Kremlin plan.

"What is necessary is for Iran to come back to the moratorium, to accept the joint venture proposal as a package that would be supported by the members of the governors' board of the IAEA," Russian Foreign Minister Sergey Lavrov told reporters in Budapest, where President Vladimir Putin was on a state visit.

The Vienna-based IAEA board of governors is to discuss the Iranian nuclear issue on Monday, and it could start a process leading to punishment by the U.N. Security Council, which has the authority to impose sanctions on Iran.

But it remains unclear if veto-wielding council members Russia and China, which have close economic and political ties with Iran, will back sanctions.

A confidential IAEA report made available to The Associated Press this week said a more than three-year-long investigation had not revealed a secret nuclear weapons program in Iran, but cautioned that a lack of sufficient cooperation from the Iranian side meant the agency could not rule it out.

The report said Iran plans to start setting up thousands of uranium-enriching centrifuges this year — a possible pathway to nuclear arms — even as it negotiates with Russia.