Iran's official news agency reports that the country's atomic energy chief says good progress has been made in nuclear negotiations with world powers, as a critical round of talks begins.

Ali-Akbar Salehi, head of Iran's Atomic Energy Organization, is heading to Lausanne, Switzerland as part of a negotiating team led by Foreign Minister Mohammad Javad Zarif. The negotiators are working to meet a self-imposed deadline for a preliminary agreement by the end of March. The talks are focused on an agreement to limit Iran's nuclear program in exchange for the lifting of harsh international economic sanctions.

The IRNA news agency quotes Salehi as saying that Tehran is seeking a win-win agreement. Zarif says that Iran will insist that all sanctions must be lifted as a condition for any nuclear deal.