U.S. and Iranian negotiators began high-stakes talks in Switzerland on Sunday aimed at hammering out the details of a broader agreement on Tehran’s nuclear program, with Iranian officials entering the discussions insisting they will not give up the country’s ability to enrich uranium.

The negotiations, led by Vice President JD Vance for the United States and Iranian parliamentary Speaker Mohammad Bagher Qalibaf and Foreign Minister Abbas Araghchi for Tehran, are the first round of talks since Washington and Tehran signed a framework agreement last week intended to end months of conflict and create a path toward a long-term nuclear accord.