Q&A-Is there a "right" to enrich uranium? Iran says yes, U.S. no

(Updates with latest from talks)

By Fredrik Dahl

GENEVA, Nov 23 (Reuters) - Disagreement over whether Iran has the right under international law to enrich uranium goes to the heart of the decade-old dispute over its nuclear programme and has complicated diplomacy to end the standoff.

Iranian officials made clear on the third day of talks in Geneva on Friday that the Islamic state's "right" to enrich uranium must be part of any interim deal aimed at curbing its atomic activity in exchange for some sanctions relief.

But diplomats at the talks in the Swiss city later said the major sticking point may have been overcome, possibly opening the way to a long-sought breakthrough.

They said new, compromise language of a deal being discussed did not explicitly recognise a right to produce nuclear fuel by any country. "If you speak about the right to a peaceful nuclear programme that's open to interpretation," a diplomat said, without elaborating.

Uranium can be used to fuel nuclear power plants - Iran's stated purpose for its atomic energy drive - but can also provide the fissile core of an atomic bomb if processed much further, which the West fears may be Tehran's ultimate aim.

Iran denies Western accusations that it is seeking the capability to build nuclear weapons.

"Iran's enrichment is non-negotiable and there is no solution without respecting Iran's right to enrichment," Foreign Minister Mohammad Javad Zarif, Tehran's chief negotiator, said this week.

The United States says no country has that explicit right under the Non-Proliferation Treaty (NPT), the 1970 global pact designed to prevent the spread of atomic bombs.

"Matters of legal theory aside, the right to enrichment has become a shorthand for the real central issue in the negotiations - whether Iran will be allowed to maintain a nuclear weapons option as part of a nuclear programme under international safeguards," Gary Samore, until recently the top nuclear proliferation expert on U.S. President Barack Obama's national security staff, wrote in a Foreign Affairs article.

WHAT DOES THE NPT SAY?

Both Iran and the United States refer to Article Four of the NPT in backing up their arguments.

While recognising every country's right to develop peaceful nuclear energy, it does not directly mention enrichment.

The NPT's opening paragraphs ban non-nuclear weapon states from developing such arms, but adds in Article Four: "Nothing in this Treaty shall be interpreted as affecting the inalienable right of all the Parties to the Treaty to develop research, production and use of nuclear energy for peaceful purposes without discrimination."