"After two years of negotiations, the United States, together with our international partners, has achieved something that decades of animosity has not: a comprehensive long-term deal with Iran that will prevent it from obtaining a nuclear weapon," Obama told reporters at the White House.
Led by the United States the so-called P5+1 countries -- the US, Britain, France, Russia, China and Germany -- reached the landmark agreement with Iran after more than 20 months of intense negotiations, mostly held in Vienna or Geneva.
For the next 15 years, Iran will not build any nuclear weapons, Obama said at the White House with Vice President Joe Biden standing by his side.
Because of this deal, Obama said Iran will remove two thirds of its installed centrifuges, the machines necessary to produce highly enriched uranium for a bomb and store them under constant international supervision.
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Iran will not use its advanced centrifuges to produce enriched uranium for the next decade. Iran will also get rid of 98 per cent of its stockpile of enriched uranium, he said.
"That means this deal is not built on trust. It is built on verification. Inspectors will have 24/7 access to Iran's nuclear facilities. Iran will have access to Iran's entire nuclear supply chain, its uranium mines and mills, its conversion facility and its centrifuge manufacturing and storage facilities," he said.
"Today, because America negotiated from a position of strength and principle, we have stopped the spread of nuclear weapons in this region. Because of this deal, the international community will be able to verify that the Islamic Republic of Iran will not develop a nuclear weapon," he said.
Well aware of the challenge that he faces in the Congress where Democrats are in a minority, Obama said, "I will veto any legislation that prevents the successful implementation of this deal.