Negotiations between Iran and six world powers on the Islamic Republic's contentious nuclear programme are beginning in Vienna this morning.

This latest round of talks is meant to build on the progress made last November when Iran said it would reduce uranium enrichment activities - the process needed to make a nuclear bomb - in return for sanctions relief.

But the Iranian government has downplayed any chances of success.

Supreme Leader Ayatollah Ali Khamenei told supporters in Tehran on Monday that he was not "optimistic" about the talks, saying they would "not lead anywhere".

Iran's Foreign Minister Mohammed Zarif said he would not give up the "nation's rights and interests", which is interpreted by some commentators as meaning the right to enrich.

Speaking at a conference of American Jewish leaders, Prime Minister Netanyahu said Iran had made "zero" compromise on its nuclear programme while receiving huge economic and business concessions in return.

British Ambassador to Israel Matthew Gould said: "The UK and Israel share the same unshakeable goal of preventing Iran from building a nuclear weapon. We are not naïve and, although we urge all sides to negotiate in good faith, we are not relying on good words, smiles or promises."