MUSCAT- Top officials from Iran and six world powers meet in Muscat Tuesday as fears grow that a hard-fought deal on Iran's nuclear programme may not be reached by this month's deadline.

The talks come after two days of discussions between US Secretary of State John Kerry and Iran's Foreign Minister Mohammad Javad Zarif ended with neither man revealing what remains unsolved in the long-running bid for a comprehensive accord.

Each laid out their demands in over 10 hours of private talks that sought to overcome deep differences, allay mutual suspicion, and bring 12 months of diplomatic brinkmanship to the point of a breakthrough.

Asked if they were making progress, as they appeared briefly for photographers, Zarif replied: "We will eventually".

Kerry said: "We are working hard. We are working hard".

On Tuesday the P5+1 powers -- made up of the five permanent UN Security Council members the United States, France, Britain, Russia and China, plus Germany -- will take part in the Muscat talks chaired by former EU foreign affairs chief Catherine Ashton, who will see out the nuclear negotiations until November 24.

The six world powers want Iran to reduce the scope of its atomic activities. In exchange, the West is offering to ease punishing economic sanctions imposed since 2012.

US President Barack Obama said Sunday that a "big gap" remained on how the West can have "verifiable, lock-tight assurances" that Iran cannot obtain a nuclear weapon.

"We may not be able to get there," Obama told CBS News.

SOURCE: AFP