Iran yesterday ignored a UN deadline to respond to an international draft deal for it to cut an atomic stockpile that the West fears could be used for weapons, and challenged the basis of the pact.

Iranian officials said they would give an answer only next week to the UN-drafted deal, which has been accepted by the other parties - Russia, France and the United States.

They also said Tehran preferred to acquire enriched uranium abroad rather than send out its own for processing into fuel for nuclear medicine, as Western powers said it had tentatively agreed to do at Geneva talks on ways to defuse growing confrontation over its disputed atomic aspirations.

Their remarks suggested that instead of engaging with the IAEA's draft, Iran was following a well-tested strategy of buying time to blunt Western pressure for harsher inter- national sanctions while it presses on with nuclear research.

The UN nuclear agency said it had been told by Iran that it was considering the proposal "in depth and in a favourable light", but needed until the middle of next week to take a position - flouting the IAEA's Friday deadline for responses.

It said IAEA Director-General Mohamed El Baradei hoped Iran's reply "will equally be positive,because approval of this agreement will signal a new era of cooperation" after seven years of standoff.

The IAEA did not say why Iran required more time to decide.

It would require the Islamic Republic, whose nuclear secrecy and restrictions on IAEA inspections have raised alarm, to send 1.2 tonnes of its known 1.5-tonne stockpile of low-enriched uranium (LEU) to Russia and France by the end of the year. There it would be further processed, in a way that would make it hard to use for warheads, and returned to Iran as fuel plates to power a Tehran reactor that makes radioactive medical isotopes but is due to run out of its imported fuel in a year.

The deal would test Iran's stated intention to use enriched uranium only for peaceful energy.

It would also gain time for broader talks on world powers' ultimate goal: that Iran allay fears that it has a secret nuclear weapons programme by curbing enrichment, in return for trade and technology benefits.

But the stance taken by Iranian officials could call into question plans to resume talks next week and offered little to douse fears of a nuclear "breakout" risk in Iran.