An interim agreement to freeze Iran's nuclear programme will enter into force on January 20, it has been announced.
The deal, agreed in talks with world powers in November, envisages easing of some international sanctions on Tehran.
US President Barack Obama welcomed the news but said more work was needed to strike a long-term deal. He threatened new sanctions if there was a breach.
The West accuses Iran of seeking nuclear weapons, but Tehran has consistently denied that.
The EU's foreign policy chief Catherine Ashton, representing the United Nations Security Council, said the world powers would now ask the United Nations' nuclear watchdog (IAEA) to verify the deal's implementation.
In return, the world powers agreed to suspend certain sanctions on trade in gold and precious metals, Iran's automotive sector, and its petrochemical exports.