US Secretary of State John Kerry and his Iranian counterpart Mohammad Javad Zarif resumed nuclear talks on Monday in Lausanne, Switzerland, to try to narrow gaps before a March 31 deadline for a political agreement.

The meeting included US Secretary of Energy Ernest Moniz and Iran's nuclear chief, Ali Akbar Salehi, who also met on Sunday to talk over technical details in curbing Iran's nuclear program.

Kerry has urged Iran to make concessions that would allow six world powers to reach a political framework agreement for a nuclear deal with Teheran that would lift sanctions in exchange for concessions on Tehran's nuclear program.