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US and Iran reach historic nuclear deal

President Obama announced Thursday a "historic understanding" with Iran that he said would prevent the country from obtaining a nuclear weapon.

Iran and major world powers reached an unprecedented agreement Thursday to begin steps to limit Iran's nuclear program in exchange for relief from economic sanctions, the result of a years-long international effort to prevent Tehran from obtaining a nuclear weapon. 

President Obama hailed the deal as a "historic understanding" just moments after top diplomatic officials in Lausanne, Switzerland, announced the framework for a final agreement on the future of the Iranian nuclear program.

"It is a good deal," Obama said Thursday in front of the White House. "If this framework leads to a final comprehensive deal, it will make our country, our allies and our world safer."

RELATED: Kerry: Foundation for ‘good deal’ with Iran

Iran and six world powers, including the United States, have been negotiating since March 26 on the nuclear program, which Iran insists is peaceful. The six nations want see limits on the program, while Iran in exchange wants punishing economic sanctions to be lifted. 

International monitors will have "unprecedented access" to Iran's nuclear facilities, Obama said. In exchange for Iran's cooperation and adherence to a final agreement, the international community will lift some sanctions, the president added.

"If Iran cheats, the world will know it," said Obama, whose remarks were broadcast live on Iranian state TV. "If we see something suspicious, we will inspect it." 

The deal would cut Iran's stockpiles of enriched uranium by 98% for 15 years, and it would cut Iran's installed centrifuges by two-thirds for 10 years, according to Secretary of State John Kerry.

Kerry also said that it would increase Iran's hypothetical "breakout time" — how long it would take Iran to speed up enrichment and produce enough fissile material for a nuclear bomb — to one year, from the current two to three months.

Negotiators had set a deadline of Tuesday for a framework, but they blew past it and kept talking. They worked through the night into Thursday, taking a break of just a few hours for sleep.

"We will not accept just any deal," Kerry said in a statement in Switzerland. "We will only accept a good deal. And today I can tell you that the political understanding with details we have reached is a solid foundation for the good deal we are seeking."

In a nod to congressional Republicans who have warned that a future administration could undo any deal with Iran, Kerry said "there will be no sunset to the deal we are workign to finalize. No sunset. None."

Federica Mogherini, the European Union foreign policy chief, called the agreement a "decisive step." In Iran, people celebrated in the streets.

Javad Zarif, the Iranian foreign minister, told reporters that the agreement demonstrates that "we can in fact solve problems, open new horizons and move forward."

Republicans, on Capitol Hill and elsewhere, were quick to slam the deal as a giveaway to Iran. Arkansas Sen. Tom Cotton, a prominent critic of the negotiations, called the framework "a list of very dangerous U.S. concessions that's going to put Iran on the path to a nuclear weapon." Presidential hopeful Jeb Bush said in a statement Thursday, "I cannot stand behind such a flawed agreement."

Arizona Sen. John McCain struck a more diplomatic tone, noting the "hard work that has been done by Secretary Kerry," but warning that the details of the agreement raised "serious questions and concerns" about the effectiveness of the plan to limit Iran's nuclear program.

"These and other issues must be addressed for any agreement to be a good agreement," McCain said in a statement Thursday. "That is why the Congress must be actively involved in reviewing and ultimately approving a nuclear agreement with Iran."