The talks suggest both sides are buying time. For Iran’s leadership, an agreement could unlock billions in frozen assets and reduce sanctions pressure.

Iran said Monday it will not accept a nuclear agreement that deprives it of what it called "peaceful activities", a reference to uranium enrichment, as it pressed the United States for guarantees it would drop sanctions.

Iran is currently reviewing a formal U.S. nuclear deal proposal as both sides remain deeply divided over uranium enrichment limits and sanctions relief.