"President Ahmadinejad said one thing to the Iranian people on Saturday and another thing to an American journalist on Monday. SoI think that all of us need to consider this with a healthy dose of skepticism," White House spokeswoman Dana Perino said at a news briefing.

Perino said the five permanents members of the UN Security Council and Germany have provided Iran "a new approach," which calls on Iran to suspend uranium enrichment and get incentives in return.

"And we would hope that they would respond in a positive way," Perino said.

Perino made the comments after Ahmadinejad, during an interview with NBC television, said Iran would respond positively if the United States could take a genuine new approach to it.

However, Ahmadinejad announced Saturday that Iran has expanded the number of uranium-enriching centrifuges to 6,000.

The United States has accused Iran of trying to develop nuclear weapons under the cover of a civilian nuclear program. However, Iran has insisted its nuclear program is for peaceful purposes only.