Munich ? Western powers pressured Tehran on Saturday to commit to a proposal designed to dispel concerns about its nuclear program, dismissing conciliatory comments from Iranian officials as mere rhetoric meant to forestall new sanctions.

U.S. Defense Secretary Robert Gates, on a trip to Turkey, said it may be time to take a “different tack” with Tehran. Other top defense officials at the Munich Security Conference rejected overtures from Iranian Foreign Minister Manouchehr Mottaki as nothing new.

The frustration reflects concerns that Iran will use the proposal only to buy more time to advance its nuclear ambitions and thwart sanctions.