That the talks are even happening represents a historic moment, given the decades of enmity between the two countries since the 1979 Islamic Revolution and the U.S. Embassy hostage crisis.

The United States and Iran are due to hold their second round of nuclear talks on Saturday, as what both sides are looking for in a deal begins to take shape.

Iran and the United States began a second round of negotiations Saturday over Tehran's rapidly advancing nuclear programme in Rome, US and Iranian officials said. The US official spoke on condition of anonymity to discuss the closed-door negotiations at the Omani Embassy in Rome's Camilluccia neighbourhood.