Iran and six world powers have agreed to carry out an interim nuclear agreement reached in November.
Iranian foreign ministry officials confirmed Sunday that the Geneva deal will take effect January 20.
Iran will limit its uranium enrichment, which the West says was being used to plan a nuclear bomb. In exchange, the United States and European Union will ease economic sanctions on Iran over the next six months.
During that time, the six world powers -- Britain, China, France, Germany, Russia and the United States -- will continue negotiations with Iran on a permanent deal.
United Nations inspectors will verify Iranian compliance.
U.S. President Barack Obama says the United States and others will give Iran "modest relief" on economic sanctions as long as it lives up to its end of the agreement.
Secretary of State John Kerry says the negotiations with Iran will be very difficult. But he says this is the best chance to resolve a critical national security issue peacefully and durably.
Mr. Obama said he will veto any new sanctions legislation passed by the U.S. Congress during talks on a long-term deal with Iran. But he said Washington will be ready to increase its sanctions if Iran fails to abide by the agreement.
The West has accused Iran of working toward building a nuclear weapon. Iran says its nuclear program is purely for generating electricity and other civilian purposes.