The U.S. wants Iran to end all uranium enrichment. The European nations have yet to make clear their position. The JCPOA limited Iran to enriching uranium up to 3.67% purity -- sufficient for civilian nuclear power purposes but below the 90% purity needed for use in a weapon.

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

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.