Iran nuclear talks intensify as sides face tough issues

Iran and major world powers have been making headway in identifying technical options for a historic nuclear deal as an end-March deadline nears but difficult issues must still be addressed, a senior U.S. official said on Tuesday.

Iran and six world powers are seeking an agreement to curb Iran's most sensitive nuclear activities for at least 10 years in exchange for a gradual end to sanctions on Tehran.

The powers -- Britain, China, France, Germany, Russia and the United States -- aim to complete the framework of a final deal by the end of March and reach a full agreement by June 30.

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