The U.N. chief hailed the Korean War armistice as the “foundation” of peace on the Korean Peninsula on the 70th anniversary of its signing Thursday, while calling for a return to negotiations on North Korea’s denuclearization.

“We need a surge in diplomacy for peace,” Secretary-General Antonio Guterres said in a statement to mark the anniversary, calling the 1953 agreement the “legal foundation for the preservation of peace and stability on the Peninsula.”