Iran will continue enriching uranium to 20 percent level to fuel "four to five" nuclear research reactors it intends to build in the "next few years," a top official told the ISNA news agency Monday.

"In the next few years, four to five (research) reactors... of 10 to 20 megawatts will be built" in the country, the head of Iran's atomic energy organisation Fereydoon Abbasi Davani was quoted as saying.

"Thus we need to continue enrichment to 20 percent in order to provide them with fuel," added Abbasi Davani, who was appointed to the post in February.

World powers accuse Iran of seeking to acquire a nuclear military capacity under the guise of its civilian atomic programme, a charge Tehran strongly denies.

Their main objection is to Iran's uranium enrichment programme, which can produce either fuel for a nuclear reactor or the fissile material for an atomic warhead.

The Islamic republic is under four sets of UN Security Council sanctions over its refusal to halt uranium enrichment.

"Enrichment up to 20 percent will continue and will not halt. We will increase the volume of the 20 percent enrichment based on the country's needs. For this, we will not ask for permission from anyone," Abbasi Davani said.

The aim of the new reactors is "to produce radio isotopes, and (to enable) research and development," he said.

These reactors "will be built in different provinces," he said, without elaborating, but adding that building the first "will take three to four years."

Iran announced in June last year it intended to build a "number" of research reactors aimed at producing radio isotopes for "sale and export to the regional and Islamic countries that need them."

At the time it said the first reactor would be built "within five years."

Abbasi Davani also confirmed that Tehran would be able to produce fuel for its functioning research reactor in Tehran "within the set timetable."

Officials have repeatedly said that Iran would produce the nuclear fuel required for a research reactor in Tehran by September 2011.

Western powers have repeatedly said Iran does not possess the technology to make the actual nuclear fuel plates required to power the Tehran research reactor which makes medical isotopes.

Abbasi Davani also said the work on Iran's second uranium enrichment plant at Fordo, southwest of Tehran, was progressing.

"The Fordo site is prepared to host centrifuges. Centrifuge machines are being built, and before installing them in Fordo, we will inform the (International Atomic Energy) Agency," he said, referring to machines which enrich uranium at supersonic speed.

The construction of Fordo plant has infuriated the West and Iran was censured in 2010 by the UN atomic watchdog over the issue, prompting strengthening of sanction against Tehran.

Iran's main uranium enrichment activities are undertaken in the central city of Natanz.