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Iranian Foreign Minister Mohammad Javad Zarif hailed the deal, which was reached after four days of hard bargaining, including an eleventh-hour intervention by Secretary of State John F. Kerry and foreign ministers from Europe, Russia and China.

"It is important that we all of us see the opportunity to end an unnecessary crisis and open new horizons based on respect, based on the rights of the Iranian people and removing any doubts about the exclusively peaceful nature of Iran"s nuclear program," Zarif told reporters in English. "This is a process of attempting to restore confidence."

The deal, intended as a first step toward a more comprehensive nuclear pact to be completed in six months, freezes or reverses progress at all of Iran"s major nuclear facilities, according to Western officials familiar with the details. It halts the installation of new centrifuges used to enrich uranium and caps the amount and type of enriched uranium that Iran is allowed to produce.

Iran also agreed to halt work on key components of a heavy-water reactor that could someday provide Iran with a source of plutonium. In addition, Iran accepted a dramatic increase in oversight, including daily monitoring by international nuclear inspectors, the officials said.

The concessions not only halt Iran"s nuclear advances but also make it virtually impossible for Tehran to build a nuclear weapon without being detected, the officials said. In return, Iran will receive modest relief of trade sanctions and access to some of its frozen currency accounts overseas, concessions said to be valued at less than $7 billion over the six-month term of the deal. The sanctions would be reinstated if Iran violates the agreement"s terms.

The Associated Press reported that hours after the accord was reached, Iran"s President Hassan Rouhani said the deal recognizes Tehran"s "rights" to maintain an atomic program.

Rouhani on Sunday repeated Iran"s claim that it would "never" seek atomic weapons.

His reference to "nuclear rights" in a nationally broadcast speech touches on the country"s demand to keep its uranium enrichment program.

In an address from the White House after the deal was announced, President Obama praised the negotiators" work. "Today, that diplomacy opened up a new path toward a world that is more secure - a future in which we can verify that Iran"s nuclear program is peaceful and that it cannot build a nuclear weapon," he said. "While today"s announcement is just a first step, it achieves a great deal. For the first time in nearly a decade, we have halted the progress of the Iranian nuclear program, and key parts of the program will be rolled back."