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A senior State Department official ruled out on Thursday the possibility of providing Iran (search) with fresh economic incentives as a means of curbing its nuclear ambitions.

"There is no reason to believe that extra incentives offered by the United States at this point would make a real difference," Undersecretary of State Nicholas Burns said.

Burns, testifying before the Senate Foreign Relations Committee, said the normal or near normal diplomatic and trade relations that European allies have maintained with Iran over the years have had little impact on Tehran's nuclear policies.

Burns said "it does not stand to reason" that a U.S. "opening of the trade gates" would encourage Iran to give up its nuclear weapons aspirations.

Burns was responding to question by committee chairman Richard Lugar, R-Ind., who mentioned economic incentives as one of four possible options for the United States in dealing with Iran.

The other three Lugar listed were regime change, military attack and a decision to accept Iran as a nuclear weapons state. Lugar did not ask Burns to discuss the merits of these possible options.

To encourage Iran to alter its nuclear policies, the United States agreed two months ago to drop opposition to Iranian membership in the World Trade Organization (search) and to allow some sales of spare parts for civilian aircraft.

The offer was made after Iran had agreed to suspend all uranium-enrichment related activities. Lately, Iran has been threatening to reverse the suspension, reinforcing concern in Washington and elsewhere that Iran remains wedded to becoming a nuclear weapons power.

Britain, Germany and France have suggested that any Iranian move to end the freeze could touch off a diplomatic process leading to U.N. Security Council (search) consideration of economic sanctions against Iran.

This would have the strong backing of the United States, which rejects Iran's contentions that its nuclear programs are aimed merely at generating electricity.

"We believe that Iran needs to face the united will of the international community," Burns said.

He said Russia has joined with Britain, Germany and France in encouraging Iran not to break the current agreement.

Iran's top nuclear negotiator, Hasan Rowhani (search), is scheduled to meet foreign ministers of the three European Union countries on May 24 to discuss the nuclear issue.