Iran is demanding the U.S. guarantee that it won't again quit the 2015 nuclear deal as the two countries prepare to resume indirect negotiations over reviving the embattled accord, its deputy foreign minister said.

"This is one of the issues that wasn't resolved in the last rounds," said Ali Bagheri Kani, who will lead Iran's negotiating team in discussions slated to recommence in Vienna on Nov. 29 after a four-month break. "In the new talks, that's one of the main tasks," he said in an interview in London on Thursday.  

Although U.S. officials have said substantial progress was made in the first six rounds of negotiations on resurrecting the pact after President Joe Biden took office, the Iranian demand is a major logjam.