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Iran nuclear deal: What happens next?

As Iran and world powers reach a historic deal over its nuclear program, how will the agreement work and what happens next?

As Iran and world powers reach a historic deal over its nuclear program, how will the agreement work and what happens next?

Is the deal finally fixed?

Not quite ... it has to win approval in Congress where it is expected to face strong opposition — particularly from Republicans.

Congress has 60 days to pick over the terms, giving opponents plenty of time to challenge the Obama administration.

The White House is already facing intense opposition from Israel, which is lobbying hard.

Related: Israel condemns agreement as ‘bad mistake’

It will also need the endorsement of Iran's supreme leader, Ayatollah Ali Khamenei, who may face opposition from hardliners.

It will then have to be ratified by United Nations Security Council.

Will sanctions be lifted immediately?

It is unlikely significant sanctions will be lifted before 2016, giving U.N. experts enough time to clear Iran of remaining suspicions about the scope of its nuclear program.

The U.N. International Atomic Energy Agency will give its verdict by December 15, its director-general Yukiya Amano said Tuesday.

Access to the Parchin military site — previously a stumbling block in talks 3 is part of a separate "arrangement", Amano added. "By December 15, 2015, the director-general will provide the final assessment on the resolution of all past and present outstanding issues," he told reporters.

Diplomats told Reuters that a U.N. arms embargo would remain in place for five years and U.N. missile sanctions would stay in place for eight years — though either could end earlier if the IAEA definitively clears Iran of any current work on nuclear weapons.

The release of frozen overseas assets, worth more than $100 billion, could come later — as well as the lifting of restrictions on Iranian institutions such as its banks and national airline.

What if Iran goes back on its word?

Iran has accepted a so-called "snapback" plan that will restore sanctions in 65 days if it violates the deal, diplomats told Reuters.