Iran struck a historic deal Sunday with the United States and five other world powers, agreeing to a temporary freeze of its nuclear program in the most significant agreement between Washington and Tehran in more than three decades of estrangement.

Iranian President Hassan Rouhani endorsed the agreement, which commits Iran to curb its nuclear activities for six months in exchange for limited and gradual sanctions relief, including access to $4.2 billion from oil sales. The six-month period will give diplomats time to negotiate a more sweeping agreement.

It builds on the momentum of the public dialogue opened during September’s annual U.N. gathering, which included a 15-minute phone conversation between President Barack Obama and moderate-leaning Rouhani, who was elected in June.

The package includes freezing Iran’s ability to enrich uranium at a maximum 5 percent level, which is well below the threshold for weapons-grade material and is aimed at easing Western concerns that Tehran could one day seek nuclear arms.

Obama hailed the pact’s provisions, which include curbs on Iran’s enrichment and other projects that could be used to make nuclear arms, as key to preventing Iran from becoming a nuclear threat.

“Simply put, they cut off Iran’s most likely paths to a bomb,” he told reporters in Washington.

Additionally, The Associated Press has learned that at least five secret meetings have occurred between top Obama administration and Iranian officials since March. The Obama administration began laying the groundwork for this weekend’s historic nuclear pact between world powers and Iran in March.

Even America’s closest allies were kept in the dark. Obama first shared the existence of the secret diplomacy with Israeli Prime Minister Benjamin Netanyahu in September, and only then offered a limited recounting of how long the discussions between Iran and the United States had been taking place.

The Obama administration then informed the other five nations negotiating alongside the U.S. — Britain, China, France, Germany and Russia. And since then much of their public diplomacy with Iran has focused on incorporating and formalizing the progress made in the private U.S.-Iranian talks.

Deputy Secretary of State William Burns and Jake Sullivan, Vice President Joe Biden’s top foreign policy adviser, led each U.S. delegation. At the most recent face-to-face talks, they were joined by chief U.S. nuclear negotiator Wendy Sherman.

It was at the final get-together that the two sides ultimately agreed on the contours of the pact signed before dawn Sunday by the so-called P5+1 group of nations and Iran, three senior administration officials told the AP. All officials spoke on condition of anonymity because they weren’t authorized to be quoted by name talking about the sensitive diplomacy.

The AP was tipped to the first U.S.-Iranian meeting in March shortly after it occurred, but the White House and State Department disputed elements of the account and the AP could not confirm the meeting. The AP learned of further indications of secret diplomacy in the fall and pressed the White House and other officials further. As the Geneva talks appeared to be reaching their conclusion, senior administration officials confirmed to the AP the details of the extensive outreach. They spoke only on condition of anonymity because they were not authorized to discuss by name the secret talks.

The Geneva deal provides Iran with about $7 billion in relief from international sanctions in exchange for Iranian curbs on uranium enrichment and other nuclear activity. All parties pledged to work toward a final accord next year that would remove remaining suspicions in the West that Tehran is trying to assemble an atomic weapons arsenal.

Iran insists its nuclear interest is only in peaceful energy production and medical research. The U.S. and Israel have regularly threatened military action if they believe Iran is about to develop a nuclear weapon.

While the agreement early Sunday — late Saturday in Washington — was concluded to great fanfare and global attention, with Secretary of State John Kerry joining fellow foreign ministers in signing the deal and Obama then presenting it to the nation in a televised White House address, the path there couldn’t have been more secret.

Congress hasn’t been notified in detail about the secret diplomacy. That could also pose a challenge for Obama, who has been waging a tense battle with Republicans and Democrats alike to prevent them from enacting new sanctions against Iran at the same time he has been offering Tehran some relief.

Several lawmakers from both parties openly scoffed Sunday at the terms of the deal between world powers and Iran. And in a reflection of the primary role played by his administration, some already are referring to the end result as Obama’s agreement. None said they had been briefed on the secret talks.

“I don’t know how to react,” Sen. Bob Corker, the Senate Foreign Relations Committee’s top Republican, said on “Fox News Sunday.” ”The administration has been trying to set the framework for these discussions for some time and I guess I’m not really particularly shocked that this has occurred.”

– Associated Press