By Frances Harrison
BBC News, Tehran
Iran has struck a basic deal to enrich uranium with Russia, Iranian state radio has reported.
Russia is helping Iran build a civilian nuclear plant
The details have still to be worked out. Tehran claimed a similar deal in February, when a Russian nuclear chief visited Iran.
Iran's ambassador to the International Atomic Energy Agency (IAEA), Ali Asghar Soltanieh, told Iranian radio he had struck a basic agreement.
Tehran is under pressure from the UN Security Council to freeze enrichment.
Mr Soltanieh said the joint enrichment company would operate on Russian soil.
But Mr Soltanieh added there was still some technical, legal and financial issues to resolve.
This is almost exactly the same thing Iran said in February. It is an attempt to revive an old Russian compromise plan which proposed moving all Tehran's sensitive nuclear work to Russia.
The problem is, Iranian officials have in the past adamantly ruled out halting enrichment research on their own soil.
The only thing that has changed now is that Iran says it has successfully managed to enrich uranium - something yet to be independently verified.
There have been some signs Iran now feels it is in a position of strength, having mastered basic nuclear technology and therefore might be more willing to consider a compromise.
But the question is whether the West is willing to bargain or insist Tehran capitulate in a way that looks humiliating to Iranians.