In testimony for Congress, Sherman held out the possibility of sanctions relief for Iran, but she made it clear the United States expected concrete actions from Tehran before this could happen and said all US concerns about Iran's nuclear program must be addressed before the core sanctions could be removed.

"We will be looking for specific steps by Iran that address core issues, including but not limited to, the pace and scope of its enrichment program, the transparency of its overall nuclear program and (stockpiles) of enriched uranium," Sherman told the Senate Foreign Relations Committee on Thursday.

"The Iranians in return will doubtless be seeking some relief from comprehensive international sanctions that are now in place," she added. "We have been clear that only concrete viable steps, and verifiable steps, can offer a path to sanctions relief."

Six major powers - Britain, China, France, Germany, Russia and the United States - will meet Iran's new negotiating team in Geneva on Oct. 15-16 to discuss its nuclear program.

The United States and its allies have imposed extensive sanctions against Iran, including a US law that forced buyers of Iranian crude to sharply cut their purchases, over its nuclear program.

At the hearing, Senate Foreign Relations Committee Chairman Robert Menendez, a Democrat, said some US lawmakers are moving forward on new US sanctions to further cut Iranian petroleum sales, but held out the possibility of sanctions relief if Iran addresses the concerns of UN Security Council.

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