Iranian and European delegations are expected to gather in Istanbul, Turkey, on Friday for fresh talks on Tehran's nuclear program, with European nations warning that a failure of negotiations may prompt punishing "snapback" sanctions on Iran.

European and Iranian diplomats have arrived in Istanbul in a renewed effort to resolve the standoff over Tehran's nuclear program. The talks mark the first formal engagement since June's 12-day war between Iran and Israel, a conflict that included U.S. airstrikes on Iranian nuclear facilities and heightened tensions across the region.