TEHRAN (Reuters) - Iran has withdrawn around $75 billion from Europe to prevent the assets from being blocked under threatened new sanctions over Tehran's disputed nuclear ambitions, an Iranian weekly said.

Western powers are warning the Islamic Republic of more punitive measures if it rejects an incentives offer and presses on with sensitive nuclear work, but the world's fourth-largest oil exporter is showing no sign of backing down.

"Part of Iran's assets in European banks have been converted to gold and shares and another part has been transferred to Asian banks," Mohsen Talaie, deputy foreign minister in charge of economic affairs, was quoted as saying.

Iranian officials were not immediately available to comment on the report in Shahrvand-e Emrouz, a moderate weekly, which did not specify the time period for the withdrawals which it said were ordered by President Mahmoud Ahmadinejad.

"About $75 billion of Iran's foreign assets which were under threat of being blocked were wired back to Iran based on Ahmadinejad's order," the weekly said.

Iran's Etemad-e Melli newspaper, also quoting Talai, last week also reported the country was withdrawing assets from European banks but did not give any figures.

On Saturday, Iran again ruled out suspending uranium enrichment despite the offer by six world powers of help in developing a civilian nuclear program if it stopped activities the United States and others suspect are designed to make bombs.

The offer -- agreed last month by the United States, Britain, Russia, China, Germany and France -- is a revised version of one rejected by Tehran two years ago.

Iran's refusal to suspend nuclear enrichment, which can provide fuel for power plants or material for weapons if refined much more, has drawn three rounds of U.N. sanctions since 2006. Tehran says it aims only to generate electricity.

EU diplomats have said the bloc is preparing an asset and funds freeze on Iran's biggest bank, state-owned Bank Melli, but that it first wants to see how Tehran responds to the new offer.

Iran is making windfall gains from record global oil prices and said in April its foreign exchange reserves stood at more than $80 billion.

Iran's foreign reserves figure has been climbing steadily. Some analysts say that, alongside rising oil revenues, Iran has been helped by its decision to shift away from the U.S. dollar into other currencies as the dollar has weakened.

Iran has made the shift as Washington has tried to isolate the Islamic state, including imposing sanctions on Iranian banks. That has pushed many Western banks to scrap dollar dealings with Iran or even end business completely.

Western countries suspect Iran is seeking the ability to make nuclear weapons. Tehran insists its secretive program is purely aimed at generating energy.

(Reporting by Parisa Hafezi; Writing by Fredrik Dahl; Editing by Ruth Pitchford)