Video: President Obama says the U.S. has agreed to provide Iran with "modest relief" from sanctions as part of a deal on the country's nuclear program

Geneva - Iran and six major powers agreed early Sunday on a historic deal that freezes key parts of Iran's nuclear program in exchange for temporary relief on some economic sanctions.

The agreement, sealed at a 3 a.m. signing ceremony in Geneva's Palace of Nations, requires Iran to halt or scale back parts of its nuclear infrastructure, the first such pause in more than a decade.

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.

Not long after the accord was reached, Iran's President Hassan Rouhani said the deal recognizes Tehran's "right" to maintain an enrichment program.

Rouhani said, "Let anyone make his own reading, but this right is clearly stated in the text of the agreement that Iran can continue its enrichment, and I announce to our people that our enrichment activities will continue as before."

But Kerry said in response on Sunday that the deal does not recognize a "right to enrich."

"There is no inherent right to enrich," Kerry said on ABC's "This Week." "And everywhere in this particular agreement it states that they could only do that by mutual agreement, and nothing is agreed on until everything is agreed on."

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."