six world powers have reached tentative agreement on sanctions relief for Tehran as part of a nuclear deal, diplomats said.
Senior officials from Iran and the six nations still have to sign off on the document outlining what sanctions will be lifted and when, sources said.
But the diplomats added that the document has been agreed by experts for both sides who have been working on details of the outline to implement the preliminary agreement reached in November 2013.
Officials had described sanctions relief as one of the thorniest disagreements between Iran and the US.
Diplomats said senior officials at the talks, who include US secretary of state John Kerry and Iranian foreign minister Mohammad Javad Zarif, still have to sign off on the package.
The word of significant progress indicates the sides are moving closer to a comprehensive accord that would end a decade of restrictions on Tehran’s nuclear programme in exchange for tens of billions of pounds in economic benefits for the Iranians.
The US and much of the world fears Iran’s enrichment of uranium and other activity could be designed to make nuclear weapons. Tehran says its programme is meant only to generate power and for other peaceful purposes.
The diplomats said the sanctions agreement was completed this week by experts from Iran and the six world powers it is negotiating with: the United States, Britain, China, France, Germany and Russia.
A senior US official did not dispute the diplomats’ account but said work remained to be done before the issue could be described as finalised.
Negotiators are striving to wrap up the deal by Monday.
Along with inspection guidelines and rules governing Iran’s research and development of advanced nuclear technology, the sanctions annex of the agreement had been among the toughest issues remaining to be resolved.
Iranian officials, including supreme leader Ayatollah Ali Khamenei, have made repeated demands for economic penalties to be lifted shortly after a deal is reached. Washington and its partners have said they would take action after Iran verifiably complies with restrictions on enrichment and other elements of the nuclear programme.