U.S. Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif are meeting Sunday in Vienna at a critical point in negotiations on Iran's nuclear program as officials report progress on two key areas in dispute, the pace of sanctions relief and the inspection of Iran’s nuclear and military facilities.
Experts are racing to resolve as many issues as possible as ministers from the six negotiating global powers return to Vienna beginning Sunday to finalize a comprehensive deal by a self-imposed July 7 deadline.
Officials in Vienna confirmed Saturday that a tentative agreement had been reached on the sanctions relief issue, but a senior U.S. administration official warned that ministers must still approve the deal.
WATCH: VOA's Mary Alice Salinas reports from Vienna
“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 U.S. official.
Late Saturday, U.S. Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif met for about an hour, but they issued no statements.
Meanwhile, the top U.N. nuclear watchdog spurred optimism about possible progress on the controversial question involving Western demands that Tehran reveal its past nuclear activities before a final comprehensive deal is reached.
Yukiya Amano, director-general of the International Atomic Energy Agency, told reporters that “with the cooperation from Iran,” he expected a complete report from his team within six months on "the possible military dimensions" (PMD) of Iran's nuclear program.
Western powers believe Iran has worked to develop nuclear weapons technology, something Tehran has denied.
Amano said that he saw progress when he visited Iran on Thursday, but that more work needs to be done.
A police officer outside the Palais Coburg where closed-door nuclear talks with Iran take place in Vienna, Austria, July 4, 2015.
All sides say a deal is within reach. But there are several outstanding issues, one of which is the IAEA's stalled investigation into the PMD.
U.S. officials in Vienna said international nuclear and sanctions experts were grinding through details of various issues. A senior U.S. State Department official said "expert groups" were taking advantage of the time during which most of the top ministers involved in talks were out of town to do the detailed, hard work involved in the process, noting that it was "clear that there are still big issues that are not resolved."
In addition to Kerry and Zarif, Chinese Foreign Minister Wang Yi remained in Vienna throughout the weekend.
WATCH: Analysts say IAEA’s Iran Visit is Key to Striking a Nuclear Deal
Some material for this report came from Reuters, AFP and AP.