Washington's UN envoy Samantha Power warned the US Congress on Monday that ratcheting up sanctions against Iran would likely torpedo negotiations on a landmark deal to curb Tehran's nuclear program.

The US ambassador to the United Nations said beefing up sanctions would also isolate the United States in its strategy to address Tehran's nuclear ambitions and weaken joint international pressure.

"Imposing new sanctions will almost certainly end a negotiations process that has not only frozen the advance of Iran's nuclear program, but that could lead us to an understanding that would give us confidence in its exclusively peaceful nature," Power said in an address to a think tank.

"If we pull the trigger on new nuclear-related sanctions now, we will go from isolating Iran to isolating ourselves," she said, speaking at a center named for Republican Senate Majority Leader Mitch McConnell.

The warning came ahead of a meeting between US Secretary of State John Kerry and Iranian Foreign Minister Javad Zarif in Geneva on Wednesday that could yield progress on the road to a historic deal on curbing Tehran's nuclear program.

The United States and its partners of the P5+1 -- Britain, China, France, Russia plus Germany -- are hoping to reach agreement with Tehran by the deadline of June 30, the third target date set to achieve a final deal.

The new Republican-controlled Congress is considering a new sanctions bill to force concessions from Iran at talks that are due to resume on January 18.

Power said the Iran nuclear talks have "produced some meaningful progress" on allowing more vigorous inspections of Iranian nuclear facilities and freezing the advance of the nuclear program.

"We are still at the negotiating table for one reason and one reason alone: we assess that we still have a credible chance of reaching the agreement we want," she said.

Under the interim deal, Iran's stock of fissile material has been diluted from 20 percent enriched uranium to five percent, in exchange for limited sanctions relief.

This would push back the "breakout capacity" to make an atomic weapon, which Iran denies pursuing.