Global powers and Iran signaled they will extend their diplomacy beyond a Nov. 24 deadline if necessary, as three days of talks aimed at curbing Tehran’s nuclear program failed to win any major breakthroughs. Senior U.S., Iranian and European diplomats stressed Tuesday that their negotiations in the Persian Gulf nation of Oman, which included direct meetings between Secretary of State John Kerry and his Iranian counterpart, Javad Zarif, solely focused on forging a comprehensive nuclear deal by late November. But diplomats involved in the Muscat talks also acknowledged that the limited advancements made here could lead the negotiators to extend their talks beyond Nov. 24.