The United States said on Saturday that Iran must choose between cooperation and confrontation after the Islamic Republic gave no clear answer at the nuclear talks over its controversial uranium enrichment program.

The Geneva talks on July 19 between Iranian security council chief Saeed Jalili and envoys from the group of six world powers - China, France, Russia, the United States, Germany and Britain - were attended for the first time by senior U.S. diplomat William Burns.

"We hope the Iranian people understand that their leaders need to make a choice between cooperation, which would bring benefits to all, and confrontation, which can only lead to further isolation," U.S. State Department spokesman Sean McCormack said after the Geneva talks.

European Union foreign policy chief Javier Solana said after the Geneva talks that the six world powers were expecting a clear answer from Tehran in about two weeks to their offer of trade and technical incentives to halt uranium enrichment.

Iran is currently under three sets of relatively mild UN Security Council sanctions for defying demands to halt uranium enrichment, which it says it needs purely for electricity generation despite Western accusations that the program is geared toward weapon production.

Iran maintains that it has never been involved in research into the development of nuclear weapons.