Agreement to freeze Iran's nuclear programme will enter into force on 20 January.

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 said the world powers would now ask the United Nations' nuclear watchdog (IAEA) to verify the deal's implementation.

Ms Ashton represents the five permanent members of the UN Security Council - US, Russia, China, France and Britain - plus Germany in the talks with Iran.

"We will ask the IAEA to undertake the necessary nuclear-related monitoring and verification activities," she said.

Under the terms of the deal, Iran has agreed to halt enrichment of uranium above 5% purity, "neutralise" its stockpile of near-20%-enriched uranium and provide daily access to inspectors.

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.

In his statement, President Obama said: "Beginning 20 January, Iran will for the first time start eliminating its stockpile of higher levels of enriched uranium and dismantling some of the infrastructure that makes such enrichment possible."

In return, he added, over the next six months the US and the other five powers would begin to implement "modest relief" so long as Iran fulfilled its obligations.

"Meanwhile, we will continue to vigorously enforce the broader sanctions regime, and if Iran fails to meet its commitments we will move to increase our sanctions," he said.

And in a warning to his critics in the US Congress, who want to impose additional sanctions, he said he would veto any legislation enacting new sanctions during the negotiations.
Ref:cnn