President Obama has hailed a deal restricting Iran’s nuclear programme as a “historic understanding” which, if implemented, will make the world safer.
The framework agreement, struck after intensive talks, aims to prevent Tehran making a nuclear weapon in exchange for phased sanction relief.
Iran and the six world powers involved must now finalise the deal.
Iranians have been celebrating in the streets but Israel says the deal threatens its survival.
“This will be a long-term deal, that addresses each path to a potential Iranian nuclear bomb,” the US President said in a statement after the deal was announced.
“If Iran cheats, the world will know it,” he said, adding that the agreement was based not on trust but on “unprecedented verification”. He said that if the deal is finalised, “we will be able to resolve one of the greatest threats to our security, and to do so peacefully”.
According to “parameters” of the agreement published by the US state department, Iran must reduce the number of its centrifuges that can be used to enrich uranium into a bomb by more than two-thirds.
It also has to redesign a power plant so it cannot produce weapons-grade plutonium, be subject to regular inspections, and agree not to enrich uranium over 3.67% – far less than is required to make a nuclear bomb – for at least 15 years.
“There’s new state of the art technology that will be used,” US Secretary of State John Kerry said. “We will have tracking of their uranium from the cradle to the grave.”