Washington and its allies shouldn't extend sanctions relief for Iran's energy sector further, the chairman of the U.S. Senate Foreign Relations Committee said.

The committee heard testimony on the effectiveness of sanctions and the diplomatic effort to curb Iran's nuclear ambitions.

Iran under the terms of a November 2013 agreement secured relief from some of the sanctions targeting its energy sector in exchange for a pledge to cut back on its nuclear research activity.

The U.S. Treasury Department said last week sanctions relief on Iran, which includes oil export provisions, is extended through November.

U.S. Sen. Robert Menendez, D-N.J. and chairman of the committee, said he didn't feel extending relief again would trigger a change of heart in Tehran.

"I will not support another extension of negotiations," he said in his opening remarks Tuesday. "At that point [after November], Iran will have exhausted its opportunities to put real concessions on the table and I will be prepared to move forward with additional sanctions."

Iran can export around 1 million barrels of oil per day under the terms of the multilateral agreement. Wendy Sherman, U.S. undersecretary for political affairs, testified that sanctions were having a dramatic effect on Iran's economy.

"We believe strongly that it is worth taking additional time to pursue these very complicated and technical negotiations," she added. "We wouldn't have agreed to an extension if we did not have an honest expectation that we have a credible path forward."