GENEVA - After the euphoria that greeted this weekend's Iran nuclear deal, the hard work begins Monday with coordinating the potentially treacherous phase of implementing the agreement and negotiating a long-term accord.
"Concrete work on the implementation will start very quickly - at different levels," a senior Western official said in Geneva where the landmark agreement was clinched in the early hours of Sunday on a fifth day of discussions.
The accord foresees what Washington called "significant limits" on Iran's nuclear programme and "unprecedented" verification by UN inspectors in exchange for modest sanctions relief.
The Islamic republic, in the third round of talks since Hassan Rouhani became president, agreed to freeze enriching uranium to fissile purities of 20 per cent, which is close to weapons-grade, for six months.
It also undertook to convert into forms much harder to process to weapons-grade its stockpile of 20-per cent material, not to install or begin operating a single new centrifuge and to idle construction work at its new Arak reactor.
Its main Natanz plant, producing low-enriched uranium, will continued operating, however.
This will all have to be verified by the International Atomic Energy Agency, the UN's nuclear watchdog, meaning a considerably bigger workload for the Vienna-based body and its Japanese chief Yukiya Amano.
The IAEA already keeps close tabs on Iran's nuclear work, with personnel frequently in the country inspecting machinery and measuring stockpiles to make sure Tehran is not diverting fissile material to make a bomb.
But under Sunday's deal this will go further, the White House says, with "daily" IAEA visits to enrichment sites and access to centrifuge assembly sites, uranium mines, and more frequent trips to Arak.
Iran will also have to provide information on plans for new nuclear facilities, descriptions of every building at nuclear sites and updated design information on the Arak reactor, according to the text of Sunday's agreement.
Mark Hibbs from Carnegie Endowment for International Peace said that of all the areas in the deal with Iran, this is one littered with potential pitfalls in the coming six months.
"This is going to be tough going," Hibbs told AFP. "Verification is where a lot of the problems are going to be."