Iran nuclear deal: John Kerry commends 'significant step'
12 January 2014 Last updated at 19:43 GMT
An interim agreement to freeze Iran's nuclear programme will enter into force on 20 January, it has been announced.
The deal, agreed in talks with world powers in November, envisages easing of some international sanctions on Tehran.
US Secretary of State John Kerry said that while implementation of the joint plan of action was an important step, the US was "very clear-eyed about the even greater challenges that we face in negotiating a comprehensive agreement".