Published: Dec 10, 2010 10:42 PM EST
Updated: Dec 10, 2010 7:47 PM EST

WASHINGTON (AP) - A senior U.S. official says the Obama administration and its European allies are prepared to place additional sanctions on Iran if it does not meet international demands to prove that its nuclear program is peaceful.

Gary Samore, the White House coordinator for weapons of mass destruction, told a Washington think tank on Friday that the U.S. and its partners will keep up pressure on Iran to come clean about its nuclear ambitions by maintaining and even expanding existing sanctions that American officials believe are already taking a toll on the Iranian economy. Samore said sanctions "will only increase if Iran avoids serious negotiations."

His comments came three days after a last round of inconclusive talks between top officials from the U.S., the E.U., Britain, France, Germany, Russia, China and Iran.

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