With only two weeks to a deadline for a breakthrough deal, senior envoys of Iran, the US and European Union met in Oman on Sunday to try to advance efforts to defuse a standoff over Tehran's nuclear programme.

Reiterating Iran's official line, Ali Akbar Velayati, a top aide to Supreme Leader Ayatollah Ali Khamenei, was quoted by Iranian media as saying the Islamic Republic would not abandon its nuclear "rights" but was committed to the negotiations under Khamenei's leadership.

Western countries and close US ally Israel suspect Iran has covertly sought to develop the means to build nuclear weapons, and a decade-long confrontation over the issue has raised the risk of a wider war in the volatile Middle East.

The discussions, between Iranian Foreign Minister Mohammad Javad Zarif, US Secretary of State John Kerry and EU envoy Catherine Ashton, aim to put verifiable limits on Iran's uranium enrichment work in return for a gradual lifting of sanctions.

Iran denies any secret nuclear weapons agenda, saying it wants peaceful nuclear energy only, but has refused to curb enrichment capacity and has been hit by damaging US, EU and UN Security Council sanctions as a result.

The thorniest unresolved issues are the size of Iran's enrichment programme, the length of any long-term agreement and the pace at which international sanctions would be phased out, according to Western diplomats involved in the negotiations.

As Kerry arrived in Oman, a senior US official said the three-way talks would be "an important meeting," with the focus on making progress in order to meet the deadline.

US officials say major gaps still remain in negotiating positions. Kerry said last week that the US and its partners were not contemplating an extension of the November 24 deadline, although he held out the possibility that negotiations could go beyond that date if major issues were resolved and there were only technical details to wrap up.

Speaking to Iranian state television on his arrival in the Omani capital Muscat on Saturday night, Zarif reiterated that sanctions imposed on Iran had brought "no result" for the West.

"If the West is interested in reaching such a solution, there is possibility to find a solution and to reach an understanding before November 24," he said.

Quoted by Iranian student news agency ISNA in Tehran, Velayati said Iran "will not abandon our rights" over nuclear facilities at Fordow, Natanz and Arak as well over the size of its centrifuge programme that enriches uranium for nuclear fuel.

Centrifuges are machines that spin at supersonic speed to increase the ratio of the fissile isotope in uranium. Low-enriched uranium is used to fuel nuclear power plants, Iran's stated goal, but can also provide material for bombs if refined much further, which the West fears may be Iran's latent aim.

"We are committed to the talks and our negotiators are acting based on a framework ... outlined by the leader," he was quoted as saying, reinforcing the widely accepted notion that Khamenei has the last word on important matters of state.

A senior Iranian official close to the talks told Reuters the Oman talks would examine "the gaps that are still huge, Iran's enrichment capacity and time frame of lifting sanctions."

Iran's ties to the West have thawed since a centrist, Hassan Rouhani, was elected president last year to try to end Iran's international isolation. But Western officials say differences remain over how to guarantee Iran's nuclear path is peaceful. - Reuters