Teams from Iran and the so-called P5+1 group of nations that includes Britain, China, France, Russia, the United States and Germany were due to hold one final meeting Tuesday morning in Vienna, followed by a news conference.
Exact details of the agreement were not publicly available ahead of an official announcement.
But the two sides have been working off a basic framework that called for ensuring Iran’s nuclear program was peaceful and not used to develop nuclear weapons. Iran has long insisted its program has only civilian purposes, and its main demand in the agreement involves the lifting of damaging economic sanctions the United Nations and individual nations have imposed during the past decade.
The negotiations in Vienna dragged past multiple deadlines as the two sides worked out important issues such as the access inspectors will have to Iranian sites in order to make sure the government is complying, as well as the pace at which the sanctions would be lifted.
Tuesday’s agreement represents a historic compromise after a 12-year standoff that has, at times, threatened to provoke a new conflict in the Middle East. It will take effect only after it clears several hurdles in Washington as well as Tehran. Conservatives in both capitals have fought against making the compromises needed to reach the agreement.
The greatest hurdle will be the U.S. Congress, where Republicans have a majority and are expected to vote against the deal after a review period of up to 60 days. President Barack Obama is expected to veto any negative vote.
Long Road to Resolution
The process to address allegations that Iran was working to develop nuclear weapons – charges it denies – has included several smaller agreements along the way, starting with an interim deal in November 2013 that curbed the country’s nuclear activity in return for limited sanctions relief.
The two sides agreed to work on a permanent deal with limits and monitoring on Iran’s nuclear program in exchange for comprehensive lifting of sanctions imposed by the United Nations and by individual countries.
That was supposed to take six months, but the process has dragged on because of debates that included the pace of lifting the sanctions, access inspectors would have to Iranian facilities, and most recently Iran’s push to have an arms embargo lifted.
VOA’s Chris Hannas contributed to this report