A top UN atomic watchdog official last week toured Iranian nuclear sites, including ones where uranium is being enriched, a senior Iranian official was quoted as saying Tuesday by Fars news agency.

Ali Asghar Soltanieh, Iran's representative to the International Atomic Energy Agency, told Fars that the head of the IAEA's nuclear safeguards division Herman Nackaerts visited the sites "last week for five days."

Nackaerts, was accompanied by his deputies, he said.

"They were taken to the Bushehr nuclear power plant, Fordo and Natanz enrichment facilities, to Isfahan nuclear installations, including the nuclear fuel rod-making plant, and to the Arak heavy water research facility and heavy water production plant," Soltanieh was quoted as saying.

The Islamic republic has been building the Arak 40-megawatt heavy water research reactor on the outskirts of the village of Khondab. Heavy water reactors do not need enriched uranium fuel in order to function.

The plant aims at supplying heavy water to be used as coolant and moderator for the research reactor, whose official function is to produce plutonium for medical research and agricultural aims.

Iran allowed UN inspectors to visit the Arak facility in August, 2009.

With the opening of the fuel plant in the central city of Isfahan Iran has mastered the complete nuclear fuel cycle from uranium mining to enrichment.

Tehran, which has been slapped with UN sanctions over its refusal to suspend nuclear enrichment, allowed the visit "to show the Islamic republic's goodwill," he added.

The team was also taken to see advanced centrifuges, Soltanieh said, adding that at the end of the tour the delegation had talks with Iran's atomic organisation chief Fereydoun Abbasi Davani.

Soltanieh said the visit was the result of meetings Abbasi Davani and Foreign Minister Ali Akbar Salehi had with IAEA chief Yukiya Amano in late June and mid-July in Vienna respectively.

"This once again shows our nation's transparent cooperation with the IAEA and the international community," Soltanieh said.

In February, Iran informed the IAEA that the Fordo plant was prepared to host centrifuges, and that it would become operational in the summer.

IAEA inspectors first visited the plant on October 25, 2009, after its disclosure by Iran to the agency triggered intense outrage in the West.

Iran's uranium enrichment work, the most sensitive part of its controversial nuclear programme, is undertaken at the Natanz facility in central Iran which is visited regularly by UN nuclear inspectors.

Enriched uranium can be used to produce both the fuel for a nuclear reactor and the fissile material for an atomic warhead.

On June 8, Abbasi Davani had announced that Iran would expand its production of 20 percent enriched uranium and eventually move the process from Natanz to Fordo.

In July, Iran said it was installing more efficient centrifuges, capable of enriching uranium at 5-6 times faster than the older machines.

Tehran says it uses the process to amass fuel material for future nuclear power plants and atomic research reactors it plans to build, dismissing fears in the West that Iran seeks to acquire a weapons capability.

The Islamic republic has over 8,000 centrifuges of the first generation IR-1, with nearly 6,000 actively purifying uranium to the 3.5 percent level, according to the latest report by the UN nuclear watchdog in May.

Iran is under four sets of UN Security Council sanctions over its refusal to suspend the uranium enrichment work, and officials in Tehran say they remain adamant to push ahead with the programme.