Diplomats said Saturday that Iran and six world powers have reached tentative agreement on sanctions relief for Tehran, among the most contentious issues in a long-term nuclear agreement that negotiators hope to clinch over the next several days.

Experts have hammered out an annex, one of five meant to accompany the agreement, outlining which U.S. and international sanctions will be lifted and how quickly.

The diplomats told The Associated Press on Saturday that the document has been agreed on by experts for both sides, who have been working on details of the outline to implement the preliminary agreement reached in November 2013.

The senior officials in the talks, which include U.S. Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif, still had to sign off on the package, a senior administration official said.

"Even if and when issues get resolved at an experts level, there will remain some open issues that can only be decided by ministers,” said the official, who asked not to be named.

Still, the word of significant progress indicated that 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 international pressure campaign 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 weren't authorized to speak publicly on this past week's confidential negotiations in Vienna, said the sanctions annex was completed this week by experts from Iran and the six world powers with whom it is negotiating: 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.

Negotiators are striving to wrap up the deal by July 7.

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 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.

U.S. officials also had been struggling to separate the "nuclear-related" sanctions they are prepared to suspend from those they wish 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 it lose its U.N. veto power, and a senior Russian negotiator said this week that his government rejected any automatic "snapback" of sanctions.

Al Jazeera and The Associated Press