By Fredrik Dahl
VIENNA (Reuters) - The head of the U.N. nuclear agency said on Wednesday he saw "no radical change" in Iran's nuclear program in the past three months, roughly since President Hassan Rouhani replaced his combative predecessor.
Yukiya Amano, director general of the International Atomic Energy Agency (IAEA), told Reuters the Islamic Republic was pursuing its most sensitive nuclear activity, enrichment of uranium to a fissile concentration of 20 percent.
But his comments suggested that between August and November Iran had not sharply expanded enrichment, which it says is peaceful but the West fears could be used for nuclear weapons.
Amano said Iran still had "quite a lot to do" to complete the Arak research reactor, a plant which is of deep concern to the West as it will be able to produce plutonium, another potential atomic bomb fuel, once it is operating.
"We do not know when this research reactor will be commissioned," he said. Iran had previously planned a start-up in the first quarter of 2014 but later postponed it.
The IAEA is expected to issue its next quarterly report on Iran - a document keenly scrutinized by Western governments - on Thursday or Friday. It will be the first that only covers developments after Rouhani took office.
"I can say that enrichment activities are ongoing ... no radical change is reported to me," Amano, a veteran Japanese diplomat, said in an interview in his office on the 28th floor of the IAEA's headquarters in Vienna.
The previous IAEA report, issued in August, showed Iran rapidly adding to its enrichment capacity by installing 1,861 IR-1 centrifuges - machines used to refine uranium - at its Natanz plant since May to reach a total of 15,416.
Amano spoke two days after Iran agreed to give his inspectors access to two nuclear-related facilities under a cooperation pact that aims to allay international concern about the country's nuclear program.
Amano said the agreement was an important first step towards clarifying all outstanding issues between the U.N. agency and Tehran, including suspicions that Iran has carried out atomic bomb research, a charge Tehran denies.
But he said implementation of the deal, which does not directly mention a stalled IAEA investigation of what it calls the possible military dimensions to Iran's nuclear program, would be key.
Western diplomats have in the past often accused Iran of stonewalling the IAEA to buy time for its nuclear program.
"The proof of the pudding is in the eating," Amano said when asked about the framework accord signed in Tehran.
The IAEA still wants access to the Parchin military base southeast of Tehran, where it believes nuclear-related explosives tests may have taken place a decade ago, as part of future steps under Monday's agreement. "We would like to visit Parchin as soon as possible," Amano said.
Iran rejects Western accusations that it is seeking the capability to make nuclear weapons. But its refusal so far to curb its program and lack of full openness with U.N. anti-proliferation inspectors have drawn tough Western sanctions.
Rouhani, a pragmatist, succeeded flamboyant hardliner Mahmoud Ahmadinejad in August, promising to try to settle the decade-old nuclear dispute and secure an easing of sanctions that have severely hurt Iran's oil-dependent economy.
NO ENRICHMENT HALT
Iran and six world powers - the United States, France, Germany, Russia, Britain and China - edged close to a preliminary nuclear accord during negotiations at the weekend and decided to meet there again on November 20.
They want Iran to halt its most sensitive nuclear work and take other measures in exchange for limited sanctions relief as part of a confidence-building deal that would buy time for negotiations on a more far-reaching diplomatic settlement.
Amano said the IAEA, which has inspectors checking Iranian nuclear facilities virtually every day of the year, would be prepared to verify the implementation of any agreement.
Asked whether the IAEA, believed to visit Iran's Natanz and Fordow enrichment sites about once a week, would quickly detect any attempt by Iran to amass weapons-grade uranium, he said:
"As far as declared facilities are concerned we have the capacity to detect any change in a timely manner."
A senior Iranian lawmaker said last month Iran had halted its 20 percent uranium enrichment - a move that would meet a main demand of the powers negotiating with Tehran - but another parliamentarian later contradicted that.
Asked whether Iran was continuing the higher-grade enrichment work, Amano said: "That's right."
Iran's higher-grade enrichment is controversial as it is a relatively short technical step to ramp it up to the 90 percent required for making a nuclear warhead. Iran says it needs the material to fuel a medical research reactor.
"There has not been that big a change," Amano said when asked about Iran's nuclear work. "On the other hand, activities which are not allowed (under U.N. Security Council resolutions calling on Iran to suspend all enrichment) are continuing".
Iran says it is refining uranium to fuel a planned network of nuclear power plants. But if enriched much further, uranium can also provide the core of a nuclear bomb.
(Editing by Alistair Lyon)