A defiant Iran said on Thursday it has told UN Security Council members that new sanctions will not affect its nuclear programme, prompting France to say Tehran was not heading in the right direction.

Tehran "considers that the adoption of such (UN) resolutions will not affect its utterly peaceful nuclear programme," the official IRNA news agency quoted Foreign Minister Manouchehr Mottaki as saying in letters to the 15 Security Council members.

Instead, Mottaki said in his letters to the countries' foreign ministers that Iran is now "more determined" than ever to develop its atomic programme.

He criticised "the hasty adoption, at the insistence of America and its allies, of an unjust and illegal resolution against the great nation of Iran."

In France, foreign ministry spokesman Bernard Valero said "very clear messages have been addressed to Iran so that it finally agrees to engage in talks on its sensitive activities."

"The letters received from Manouchehr Mottaki are not going in the right direction. What we expect from Iran is that it addresses the concerns of the international community with concrete measures," he said.

On June 9, 12 members of the Security Council, including all five permanent members, voted in favour of imposing a fourth set of sanctions on Tehran over its uranium enrichment programme, the most controversial aspect of the nuclear drive.

Brazil and Turkey, which had brokered a nuclear swap deal with Iran in May, voted against and Lebanon abstained.

Mottaki thanked Turkey and Brazil for "resisting the pressure of some specific nations and voting against the resolution," IRNA said.

He also reiterated Tehran's position that "nuclear weapons have no place in Iran's defence and security policies."

World powers led by Washington accuse the Islamic republic of seeking to build nuclear weapons and are demanding that it freeze its uranium enrichment activity, which can be a key step towards developing an atomic arsenal.

Iran insists its nuclear programme is for peaceful purposes only.

Last month, CIA director Leon Panetta warned that Iran has enough low-enriched uranium to make two weapons, which it could have prepared and ready for delivery as early as 2012.

"We think they have enough low-enriched uranium for two weapons," Panetta told ABC television's "This Week" program.

Tehran would need a year to enrich it fully to produce a bomb and it would take "another year to develop the kind of weapon delivery system in order to make that viable," he said.

The new UN measures against Tehran authorise states to conduct high-seas inspections of vessels believed to be ferrying banned items to Iran and add 40 entities to a list of people and groups subject to travel restrictions and financial sanctions.

Meanwhile, US President Barack Obama was expected on Thursday to sign a separate US package of tough new energy and financial sanctions on Iran, over and above those approved by the UN Security Council.

The US Senate and the House of Representatives approved the legislation last week by crushing 99-0 and 408-8 margins, respectively.

Iran's parliament speaker Ali Larijani told reporters in Syria on Thursday the US sanctions were "meaningless" and would have "little impact on Iran."

Larijani, formerly Iran's top nuclear negotiator, accused the United States of pressuring Iran to give up support for the Palestinian cause, saying that would never happen.

The new measures aim to choke off Iran's access to imports of refined petroleum products like gasoline and jet fuel and curb its access to the international banking system.

The European Union too slapped a separate set of sanctions on Iran soon after the UN measures were imposed.

Meanwhile, the UN nuclear watchdog said Thursday its top investigator Olli Heinonen, head of the agency's long-running investigations into Iran and Syria, would step down next month "for personal reasons."