CNN : Deal reached on Iran nuclear program, diplomats say....The Deal Is Far From Over. The accord is expected to face fierce opposition from Republicans in the U.S. Congress, as well as from Israeli Prime Minister Benjamin Netanyahu, a longstanding critic of the negotiations.

Vienna (CNN)After 20 months of tortuous talks, negotiators have reached a historic deal aimed at reining in Iran's nuclear program, diplomats said Tuesday.

The agreement, a focal point of U.S. President Barack Obama's foreign policy, appears set to reshape relations between Iran and the West, with its effects likely to ripple across the volatile Middle East.

Representatives of Iran, the United States and the other nations involved in the marathon talks will hold a final meeting in Vienna on Tuesday, officials said.

After that, an official statement on the agreement is expected to be issued by Iran and the European Union, the diplomats said.

Leaders of the Western nations involved in the talks have backed a deal as the best way to stop Iran from becoming a nuclear power.

Iran, meanwhile, has been eager to get rid of international economic sanctions that have been squeezing its economy.

The essential idea behind the deal is that in exchange for limits on its nuclear activities, Iran would get relief from sanctions while being allowed to continue its atomic program for peaceful purposes.

Far from over

But the deal, brokered during lengthy negotiations in a Vienna hotel, is far from the end of the story.

Details on what terms were agreed on key technical issues weren't immediately available Tuesday.