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.

Iranian and European delegations will gather in Istanbul, Turkey, on Friday for fresh talks on Tehran's nuclear program.

Iranian diplomats said they held "frank and detailed" nuclear talks on Friday with counterparts from Germany, Britain and France, who have threatened to trigger sanctions if Tehran fails to agree a deal on uranium enrichment and cooperation with UN inspectors.