VIENNA — After long, fractious negotiations, world powers and Iran struck a historic deal Tuesday to curb Iran’s nuclear program in exchange for billions of dollars in relief from international sanctions — an agreement aimed at averting the threat of a nuclear-armed Iran and another U.S. military intervention in the Middle East.

The accord marks a dramatic break from decades of animosity between the United States and Iran, countries that alternatively call each other the “leading state sponsor of terrorism” and the “the Great Satan.”

“This deal offers an opportunity to move in a new direction,” President Barack Obama said in early morning remarks from the White House that were carried live on Iranian state television. “We should seize it.”

In Tehran, Iranian President Hassan Rouhani said “a new chapter” has begun in his nation’s relations with the world. He maintained that Iran had never sought to build a bomb, an assertion the U.S. and its partners have long disputed.

Beyond the hopeful proclamations from the U.S., Iran and other parties to the talks, there is deep skepticism of the deal among U.S. lawmakers and Iranian hardliners. Obama’s most pressing task will be holding off efforts by Congress to levy new sanctions on Iran or block his ability to suspend existing ones.

Sunni Arab rivals of Shiite Iran have also expressed concern over the deal. And Israel, which sees Iran as an existential threat, strongly opposes leaving the Islamic republic with nuclear infrastructure in place.

Israeli Prime Minister Benjamin Netanyahu, who has furiously lobbied against a deal, called the agreement a “bad mistake of historic proportions.”

The nearly 100-page accord announced Tuesday aims to keep Iran from producing enough material for an atomic weapon for at least 10 years and impose new provisions for inspections of Iranian facilities, including military sites.

The deal was finalized after more than two weeks of furious diplomacy in Vienna. Negotiators blew through three self-imposed deadlines, with top American and Iranian diplomats both threatening at points to walk away from the talks.

Secretary of State John Kerry, who did most of the bargaining with Iranian Foreign Minister Mohammad Javad Zarif, said persistence paid off. “Believe me, had we been willing to settle for a lesser deal we would have finished this negation a long time ago,” he told reporters.

The economic benefits for Iran are potentially massive. It stands to receive more than $100 billion in assets frozen overseas, and an end to a European oil embargo and various financial restrictions on Iranian banks.

The breakthrough came after several key compromises.

Iran agreed to the continuation of a U.N. arms embargo on the country for up to five more years, though it could end earlier if the International Atomic Energy Agency definitively clears Iran of any current work on nuclear weapons. A similar condition was put on U.N. restrictions on the transfer of ballistic missile technology to Tehran, which could last for up to eight more years, according to diplomats.

Washington had sought to maintain the ban on Iran importing and exporting weapons, concerned that an Islamic Republic flush with cash from sanctions relief would expand its military assistance for Syrian President Bashar Assad’s government, Yemen’s Houthi rebels, the Lebanese militant group Hezbollah and other forces opposing America’s Mideast allies such as Saudi Arabia and Israel.