(FILES) In this December 22, 2014 file photo, US Ambassador to the United Nations Samantha Power talks during a Security Council meeting regarding human rights violations in North Korea at the United Nations in New York. Washington’s UN envoy Samantha Power warned the US Congress on January 12, 2015 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. AFP PHOTO/ DON EMMERT / FILES