Written by technical experts, the document still must be approved by senior officials of the seven nations at the table, including U.S. Secretary of State John Kerry, Iranian Foreign Minister Mohammad Javad Zarif and the foreign ministers of the five other countries expected to join Kerry and Zarif in Vienna this weekend for a push to meet a July 7 deadline.
The development indicated the sides were moving closer to a comprehensive accord that would set a decade of restrictions on Tehran's nuclear program in exchange for tens of billions of dollars in economic benefits for the Iranians.
Officials had described sanctions relief as one of the thorniest disagreements between Iran and the United States, which has led the campaign of international pressure against Iran's economy. The U.S. and much of the world fears Iran's enrichment of uranium and other activity could be designed to make nuclear weapons; Iran says its program is meant only to generate power and for other peaceful purposes.
The diplomats, who spoke on condition of anonymity because they weren't authorized to speak publicly on this past week's confidential negotiations, said the sanctions annex was completed this week by experts from Iran and the six world powers in the negotiations: the United States, Britain, China, France, Germany and Russia. They did not provide details of the agreement.
A senior U.S. official did not dispute the diplomats' account but said work remained to be done on "Annex II" before the issue could be described as finalized. And beyond a political agreement that was still in the draft stage, details also needed to be finalized on tough issues contained in four other appendices.
They include inspection guidelines, rules governing Iran's research and development of advanced nuclear technology and the nuts and bolts of reducing the size and output of Iran's uranium enrichment program.
As part of a deal, the Obama administration also wants Iran to fully co-operate with the U.N.'s International Atomic Energy Agency's investigation of allegations that Tehran worked secretly on nuclear arms — something Iran vehemently denies. But chances of progress on that issue appear to be dimming.
IAEA chief Yukiya Amano told reporters on Saturday that "more work will be needed" to advance the probe, in a statement similar to previous ones from his agency, which has struggled for nearly a decade to resolve its concerns.
While saying he could wrap up his investigation by the end of the year, Amano said he needs Tehran's co-operation to do so. Iranian President Hassan Rouhani said after Thursday's meeting in Tehran with Amano that the agency now understands that the "pointless allegations" are "baseless."
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'd take action after Iran verifiably complies with restrictions on enrichment and other elements of the nuclear program.
Much of the negotiation on the matter has concerned sequencing, so that both sides can legitimately claim to have gotten their way.
Several other matters related to sanctions also had posed problems.
The Obama administration cannot move too quickly to remove economic penalties because of Congress, which will have a 30-day review period for any agreement during which no sanctions can be waived.
American officials also had been struggling to separate the "nuclear-related" sanctions it is prepared to suspend from those it wishes to keep, including measures designed to counteract Iranian ballistic missile efforts, human rights violations and support for U.S.-designated terrorist organizations.
And to keep pressure on Iran, world powers had been hoping to finalize a system for snapping suspended sanctions back into force if Iran cheats on the accord. Russia has traditionally opposed any plan that would see them lose their U.N. veto power and a senior Russian negotiator said only this week that his government rejected any automatic "snapback" of sanctions.
Associated Press Diplomatic Writer Matthew Lee contributed to this report.