Should diplomacy collapse, Washington and Jerusalem would be positioned to justify military action against Iran as a last resort.

Iran says its nuclear programme is for civilian purposes only. It insists it is not trying to develop nuclear weapons, but many countries - as well as the global nuclear watchdog, the International Atomic Energy Agency (IAEA) - are not convinced.

The high-stakes talks over the future of Iran’s nuclear program come amid escalating tensions in the region and a buildup of U.S. military assets.