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.

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.

President Donald Trump warned on Monday that he would order fresh U.S. attacks on Iran's nuclear facilities should Tehran try to restart facilities that the United States bombed last month. Trump issued the threat as he held talks with British Prime Minister Keir Starmer at his Turnberry golf resort on the western coast of Scotland.