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.

Three European powers met with an Iranian minister to try to reopen negotiations over the limits of its nuclear activities.

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.