In a speech at the McConnell Center at the University of Louisville, Power said that the talks with Iran had not reached a point at which the risks of negotiating exceeded the benefits, and that there was still a chance of reaching an agreement.
"If new sanctions were imposed, Iran would be able to blame the United States for sabotaging the negotiations and causing the collapse of the process," she said.
The last round of negotiations on Iran's controversial nuclear program failed to meet its November 2014 deadline for a permanent settlement. However, Tehran and the so-called P5+1 -- the U.S., U.K., France, China and Russia plus Germany -- agreed to extend nuclear talks until end of July 1, voicing optimism that remaining disputed points can be resolved.
World powers suspect Iran is seeking to acquire nuclear weapons and have imposed targeted economic sanctions since 2006. Iran insists its uranium enrichment program is for peaceful purposes only.
"Some members of Congress believe that the time has come to ratchet up sanctions on Iran," Power said. "If we pull the trigger on new nuclear-related sanctions now, we will go from isolating Iran to potentially isolating ourselves."
Tehran agreed to limit certain aspects of its controversial nuclear program in exchange for some relief in international sanctions under a deal reached in Nov. 2013 in Geneva.
Western countries in turn eased some of the economic sanctions imposed during the dispute.
"Sanctions did indeed help to bring Iran to the negotiating table," Power said. "But sanctions did not stop the advance of Iran’s nuclear program. Negotiations have done that."
The next talks between Iran and the P5+1 will be held in Geneva on Jan. 18.