"We are going to continue as long as there is no legally-binding instrument for assurance of supply," Ali Asghar Soltanieh, Iran's ambassador to the International Atomic Energy Agency (IAEA), told reporters after a conference in Brussels.

Asked whether Iran would end its controversial uranium enrichment programme if such a guarantee were in place, Soltanieh said it would first have to be shown to be effective.

"It is not only the piece of paper, you have to practise... the plan," he said.

"We had a contract with the US and they did not fulfill their obligations... Germany had a contract and they did not."

Enrichment is at the heart of Western fears that Iran could be seeking nuclear weapons as it can be diverted to make the fissile material for an atomic bomb as well as fuel for nuclear power plants.

The UN has already applied sanctions over the issue but Tehran insists its nuclear programme is strictly peaceful and solely aimed at generating electricity and has refused to suspend uranium enrichment.

Six major powers -- Britain, China, France, Germany, Russia and the United States -- have put forward the possibility of a package of technological, economic and political incentives if it suspends uranium enrichment.

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