"A deadline is not an issue. We think such statements are not constructive and they will not help resolving the problem. We will respond next month," foreign ministry spokesman Hamid Reza Asefi told reporters.

World powers gave Iran one more week Thursday to provide a "clear and substantive response" to an international proposal on suspending uranium enrichment.

The five permanent UN Security Council members -- Britain, China, France, Russia and the United States -- plus Germany have offered Iran a package of incentives that includes multilateral talks if it agrees to temporarily halt enrichment.

That work is at the centre of fears the hardline regime could acquire nuclear weapons, although Tehran insists the project aims only to provide fuel for nuclear energy.