WASHINGTON/TEHRAN - The United States signaled on Thursday its patience with Iran was wearing thin, saying Tehran was rapidly approaching a December deadline to accept a U.N.-brokered nuclear deal with Western powers.

Adding to the growing international pressure on Iran over its nuclear program, German Chancellor Angela Merkel said our patience is being sorely tested and that fresh sanctions must be considered if Iran continued to rebuff the U.N. proposal.

The warnings from Washington and Berlin came in a week in which Tehran announced plans to build 10 uranium enrichment plants in a major expansion of its atomic program and Iranian President Mahmoud Ahmadinejad said he saw no further need for talks with the West.

Iran's official IRNA news agency said parliament would review relations with countries that voted against Iran's nuclear activities at the International Atomic Energy Agency last week.

The IAEA board angered Iran by censuring it for covertly building a second uranium enrichment plant near the holy city of Qom, in addition to its main IAEA-monitored one at Natanz. The nuclear watchdog called for a halt to construction.

The United States and its allies suspect Iran is secretly using its nuclear program as a cover to develop atomic weapons, a charge Iran denies. Under the U.N.-brokered deal, Iran would send the bulk of its low-enriched uranium abroad for processing and conversion into fuel for a civilian reactor.

In talks with six world powers in Geneva on October 1, Iran agreed in principle to the deal but has since balked. Iran has until the end of the year to agree to it or face the threat of tougher sanctions.

Time is running out, White House spokesman Robert Gibbs said, adding that Iran's apparent decision to walk away from the October 1 deal spoke volumes.

AFTER DECEMBER, WHAT NEXT?

If the December deadline passes, the U.N. Security Council is expected to begin looking at steps toward imposing fresh sanctions on Iran.

Russia, which has a veto in the Security Council, has seemed increasingly prepared to support some tightening of sanctions as a last resort.

But on Thursday, Prime Minister Vladimir Putin, while declining to answer a question on sanctions, told reporters that Russia had no information that Iran is working on the creation of a nuclear weapon.

U.S. President Barack Obama's efforts to engage Iran with confidence-building measures have so far been fruitless.

Nothing they (Iran) have done to date would seem to suggest they are ready to take this opportunity, a senior U.S. administration official said, referring to the U.N. deal.

We are not going to allow them to let the clock tick. Regardless of what they are trying to do, we have our timeline.

On Wednesday, Ahmadinejad said Iran would purify its uranium stockpile to the level needed for a medical reactor in Tehran -- in Western eyes a big step toward the highly enriched uranium needed for a nuclear warhead.
For some Iran watchers, the announcement appeared to sound the death knell for a deal but the U.S. official dismissed Ahmadinejad's recent statements as bluster aimed at a domestic audience after the IAEA censure.

It doesn't really much matter what Ahmadinejad and others are saying out of Iran. What matters ultimately is action, the U.S. official said.

In an unusual step, the White House urged Tehran on Thursday to help locate an American citizen, Robert Levinson, who went missing during a business trip to the Iranian island of Kish in March 2007. Iran has only confirmed detaining three U.S. hikers on spy charges.

(Writing by Kevin Liffey and Ross Colvin; additional reporting by Matt Spetalnick in Washington; Editing by John O'Callaghan)

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