Leading nations have agreed to offer more incentives to Iran to encourage the suspension of its nuclear programme. The group of six mediators, which includes Russia, says it's an updated package originally offered and rejected by Iran in 2006.

The details of the new proposal were not revealed.

The joint move is another attempt to persuade Iran to halt its controversial nuclear programme by providing economic benefits.

The mediators said they hope for a swift response.

Meanwhile, Robert Lowe, the Manager of the Middle East Programme at Chatham House, a leading UK-based think-tank, says “it’s highly unlikely that there will be a significant breakthrough” any time soon.  He said: “the various parties remain too far apart”.

“There’s a bigger, more fundamental stand-off here between Iran and the U.S. It goes back decades. Both sides are very proud and have a sense of discontent and injustice with the other. Before there’s a major shift a major mindset change on both sides, it’s very hard to see any progress,” he said.

“Furthermore, with the campaigning in the U.S. presidential election coming up later this year, it’s very unlikely that there will be anything major developed until 2009, when we’ll have a new U.S. president who can actually maintain a coherent policy,” the analyst added.