An interim nuclear deal between Iran and six world powers and Iran will start on 20th January, the EU's foreign policy chief Catherine Ashton said.
Ashton represents the six nations - the United States, Russia, China, France, Britain and Germany - in diplomatic contacts with Iran related to the nuclear standoff.
She said the sides would now ask the United Nations' nuclear watchdog to verify the deal's implementation.
"We will ask the IAEA to undertake the necessary nuclear-related monitoring and verification activities," she said.
Under the agreement, Iran has promised to curb its most sensitive nuclear activities in return for some relief from Western economic sanctions.
More top news
"Our ability to pre-empt or respond to threats will be eroded if we don't keep up with our adversaries."
"You are one of the silence breakers and we all owe you a debt of gratitude."
Maximum temperature 11 C (52 F).