The UN atomic watchdog will likely say today that Iran has complied with last July's landmark deal with major powers aimed at putting a nuclear bomb out of Tehran's reach, diplomatic sources said.
The International Atomic Energy Agency report will allow US Secretary of State John Kerry and his Iranian and EU counterparts, Mohammad Javad Zarif and Federica Mogherini, to announce in Vienna that the deal can enter into force, the sources said.
Under the July 14 deal, Iran agreed to scale down dramatically key areas of its nuclear activities in exchange for relief from painful sanctions, notably on Tehran's lifeblood oil exports.
These steps, combined with ultra-close IAEA inspections, extend to at least one year - from just a few months previously - how long Iran would need to make one nuclear bomb's worth of fissile material.
Iran has always denied wanting nuclear weapons, saying its activities are exclusively for peaceful purposes such as power generation.
The hard-fought agreement was sealed in Vienna by Kerry, Zarif, Mogherini and the foreign ministers of Russia, China, Britain, France and Germany after two years of rollercoaster negotiations following the June 2013 election of moderate Iranian President Hassan Rouhani.
The highly complex deal drew a line under a standoff dating back to 2002 marked by several failed diplomatic initiatives, ever-tighter sanctions, defiant nuclear expansion by Iran and threats of military action.
In addition it put the Iran and the US on the road to better relations some 35 years after the Islamic revolution that topped the US-backed Shah, and at a particularly explosive time in the Middle East.
The agreement, heralded as US President Barack Obama's biggest - and some might say only - major foreign policy triumph, has by no means been universally cheered, however.
Obama's Republican opponents charge that it fails to do enough to ensure Iran will never get the bomb, a complaint shared by Israel, Iran's arch foe widely assumed to have nuclear weapons itself.
Sunni Saudi Arabia, Iran's other great regional rival, is also alarmed at the prospect of warmer US-Iran ties and of predominantly Shiite Iran, newly flush with oil revenues, increasing its influence.
