"Today could have been the end of hope," he said, "but now we are starting a new chapter of hope."
The breakthrough comes after months of thorny negotiations between Iran and the so-called P5+1 group -- the five permanent members of the U.N. Security Council and Germany.
Under the deal, Tehran’s nuclear ability would be significantly limited for more than a decade, The New York Times reported. In return, the six world powers would agree to lift international oil and financial sanctions against Iran
Tehran would also allow inspectors from the U.N's International Atomic Energy Agency to seek visits to Iranian military sites as part of their monitoring duties, a senior diplomat told The Associated Press. However, such visits could be denied or delayed by the Iranian government. In such cases, an arbitration board composed of Iran and the six world powers would have to be convened to determine the right of access.
The deal is the culmination of years of delicate negotiations between formerly bitter enemies U.S. and Iran, as well as negotiators from China, France, Russia, the United Kingdom and Germany.
For more than a decade, international powers have raised concerns that Tehran is using its nuclear enrichment program to build a nuclear weapon. Iran says the program is solely for peaceful purposes such as energy and medicine.
International sanctions imposed over the country’s nuclear work have hampered Iran's economy and in 2013 Tehran agreed to freeze some nuclear activities in exchange for partial sanctions relief.
The 2013 agreement, the first between Iran and the U.S. in more than three decades, paved the way for a framework agreement in April, and Tuesday's comprehensive nuclear accord.
The deal still faces several hurdles. Opponents of the talks in the U.S. Congress have vowed to thwart any agreement that they deem has not gone far enough to prevent an Iranian nuclear bomb. Congress now has 60 days to review the deal before President Barack Obama can start removing congressional sanctions. Iran says it won't implement its end of the deal until sanctions are removed and supporters of the nuclear accord fear that prolonged delays could strengthen hardliners in Washington and Tehran.
The deal also has its detractors all over Iran’s neighborhood. The most outspoken of them is Israel, whose leaders have fought hard to obstruct a nuclear accord. They saythe deal’s lax restrictions will actually help Iran build a bomb, while sanctions relief will allow Iran to funnel more funds to terrorist groups in the region.
Gulf powers, including Saudi Arabia and the United Arab Emirates, are also wary that their longtime rival will be strengthened by a rapprochement with the international community and have quietly voiced their concerns that a deal with Iran would tip the balance of power in the region.