Citing unnamed officials, the New York Times said on Tuesday that the Russian national security head, Igor Ivanov, delivered the ultimatum last week to Iran's deputy chief nuclear negotiator Ali Hosseini Tash.

"I deny this report," Hosseini Tash told state radio.

"It was completely the opposite. Mr Ivanov was trying to convince us that the issue of Bushehr plant is not linked to the nuclear dossier," he said.

Moscow infuriated Tehran last week by cancelling its March deadline to deliver fuel for the much-delayed Bushehr plant it is building in the south of the country because Iran had not met its financial commitments.

Iran denied the charge, insisting it had paid beyond the agreed amount.

The United States, which accuses Iran of seeking to develop nuclear weapons under the guise of a civilian programme, has urged Russia to cut off assistance for Iran's Bushehr plant.

The report came as the UN Security Council was set to review a draft resolution that would toughen punitive measures against Iran for its refusal to suspend enrichment.

The Security Council imposed sanctions on Iran's nuclear and missile programmes in December after it failed to freeze uranium enrichment, the process which can be used to make nuclear fuel as well as atomic weapons.

Iran says its nuclear programme is solely aimed at peaceful energy ends.

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