Iran trumpeted advances in nuclear technology on Wednesday, citing new uranium enrichment centrifuges and domestically made reactor fuel, in a move abetting a drift towards confrontation with the West over its disputed atomic ambitions.

The nuclear declaration comes alongside a decision to 'revise' oil sales to six European Union countries in retaliation for an EU ban on its petroleum exports.

"Today the ambassadors of some European countries were called in by the foreign ministry, where it was insisted to them that Iran will revise its oil sale to these countries," website IRIB reported without giving further details.

The countries targeted were France, Greece, Italy, the Netherlands, Portugal and Spain, it said.

The nuclear announcement meanwhile, underlined Iranian determination to pursue a nuclear programme its Islamic clerical rulers see as a pillar of power, protection and prestige despite Western sanctions that are inflicting increasing damage on Iran's oil-based economy.

Iran has been resorting to barter to import basic staples as sanctions, imposed over its pursuit of nuclear activity seen in the West as geared to developing atomic bombs, have spread to block its oil exports and central bank financing of trade.

Tehran has for some years been developing and testing new generations of centrifuges to replace an outdated, breakdown-prone model. In January it said it had successfully manufactured and tested its own fuel rods for use in nuclear power plants.

The aim of its announcements on Wednesday was to show that international sanctions are failing to stop it making progress in nuclear know-how despite trade embargoes and to strengthen its hand in any renewed negotiations with six world powers.

"The fourth generation of domestically made centrifuges have a higher speed and production capacity ... It will be unveiled on Wednesday," state television said, without giving a source.

It was the latest display of Iran thumbing its nose at a series of U.N. resolutions demanding that it suspend uranium enrichment and open up to U.N. nuclear inspectors.

Last year, Iran installed two newer models for large scale testing at a research site near the central town of Natanz. But it remains unclear whether Tehran, subject to increasingly strict trade sanctions, has the means and components to make the more sophisticated machines in industrial quantity.

If Iran eventually succeeded in introducing modern centrifuges for production, it could significantly shorten the time needed to stockpile enriched uranium, which can generate electricity or, if refined much more, nuclear explosions.

Tehran has worked for several years to perfect faster, more reliable centrifuge machines than the 1970s-vintage P-1 model it now uses to refine uranium.

Western analysts were sceptical of the proclaimed advances.

"We have seen this before. We have seen these announcements and these grand unveilings and it turns out that there was less there than meets the eye. I suspect this is the same case," said Shannon Kile at the Stockholm International Peace Research Institute (SIPRI).

No change in course

The United States and Israel have not ruled out military action if diplomacy and sanctions are ultimately judged futile in reining in Tehran's nuclear activity.

Iran has threatened retaliation for any attack or effective ban on its oil exports, suggesting it could seal off the main Gulf export shipping channel, the Strait of Hormuz, used by a third of the world's crude oil tankers.

Iranian officials have refused to negotiate curbs on the programme, saying it aims solely to produce electricity for booming domestic demand in OPEC's No. 2 oil-exporting state.

A senior Iranian official said Iran would load domestically made nuclear fuel rods into its Tehran Research Reactor on Wednesday for the first time to keep it running.

"The first home-made nuclear fuel rods will be loaded in the Tehran Nuclear Research Reactor in the presence of the president," Ali Baqeri, deputy head of Iran's Supreme National Security Council, told ISNA.

The Tehran reactor produces radio-isotopes for use in medical treatments and agriculture.