World powers and Iran have reached a landmark deal to curb the Islamic Republic's nuclear programme in exchange for sanctions relief, after an 18-day marathon negotiations in Vienna.

The accord was announced on Tuesday by Iranian Foreign Minister Mohammad Javad Zarif and the European Union's policy chief Federica Mogherini in a joint statement in the Austrian capital.

Iranian Foreign Minister Mohammad Javad Zarif called the deal a "win-win" solution to end "an unnecessary crisis and open new horizons for dealing with serious problems that affect our international community."

"I believe this is a historic moment. We are reaching an agreement that is not perfect for everybody but it is what we could accomplish and it is an important achievement for all of us," said Zarif.

"Today could have been the end of hope on this issue, but now we are starting a new chapter of hope."