TEHRAN Iran began loading fuel into the core of its first nuclear power plant on Tuesday, its atomic energy chief said, the last major step toward realizing its stated goal of becoming a peaceful user of nuclear energy.
Officials said the fueling at the Bushehr plant showed Iran's nuclear plans were on track despite sanctions aimed at forcing it to curb uranium enrichment that many countries fear is aimed at developing atomic bombs.
The head of the U.N. nuclear watchdog called on Iran, the world's fifth largest oil exporter, to address concerns about its true intentions. Several European energy companies said they were reducing their dealings with the Islamic Republic due to sanctions.
"This day will be remembered ... because it was the day when fuel was lowered into the core of the reactor," said Ali Akbar Salehi, head of Iran's Atomic Energy Organization.
U.S. Secretary of State Hillary Clinton said Washington has no problem with the Russian-built Bushehr plant but does with other sites where weapons work may be going on.
"Our problem is with their facilities at places like Natanz and their secret facility at Qom and other places where we believe they are conducting their weapons program," Clinton told reporters at a meeting with Austrian Foreign Minister Michael Spindelegger.
"They are entitled to peaceful civilian nuclear power. They are not entitled to nuclear weapons."
Amid great media fanfare, fuel rods were transported into the reactor building in August but they were not inserted into its core and the plant's start-up was delayed due to what were described as minor technical problems.
At a much lower-key news conference, broadcast live from the plant on Iran's coast, Salehi said it would take another two months to complete the process of lowering 163 fuel assemblies into the core of the reactor and running tests. He said three fuel assemblies had been inserted so far.
The 1,000-megawatt plant will feed Iran's first nuclear power into the national grid early next year, he said.
"If it were in Europe it would supply electricity to about 800,000 or 900,000 people," said Ian Hore-Lacy of the World Nuclear Association industry body.
Iran has denied the "Stuxnet" computer virus delayed the start-up, although it did infect some computers at Bushehr. Some analysts speculated the worm was designed by Iran's enemies to sabotage the nuclear program.
"Iran's peaceful nuclear activities are going on as scheduled," Foreign Ministry spokesman Ramin Mehmanparast told reporters.
Alaeddin Boroujerdi, the head of Iran's parliamentary committee on foreign policy and national security, called the fueling of Bushehr a victory against sanctions.
"What counts a lot in this process is that America mobilized all its resources across the world to ratchet up the pressure on the Islamic Republic of Iran and they believe that imposing sanctions on us will deter us from making progress," he said.
A U.N. Security Council resolution passed in June, imposing a fourth round of sanctions, renewed a call on Iran to suspend uranium enrichment, something Tehran has explicitly refused to do, saying such activity is its right under international law.
Speaking in Moscow, the chief of the U.N. nuclear agency urged Iran to allay concerns about its nuclear aims.
"I am requesting Iran take concrete steps, concrete measures toward the full implementation of their obligations," said International Atomic Energy Agency chief Yukiya Amano.
Iran insists it needs to enrich uranium -- material which also can be used to make weapons if refined to a high degree -- to fuel future power stations and a medical research reactor.
Experts say firing up the $1-billion Bushehr plant will not take Iran any closer to building a nuclear bomb since Russia will supply the enriched uranium for the reactor and take away spent fuel that could be used to make weapons-grade plutonium.
Fueling Bushehr "should not be interpreted as some kind of act of defiance," said Mark Fitzpatrick at the International Institute for Strategic Studies in London.
"Nobody has asked them to stop on Bushehr. I think it is a big mistake to equate these two issues," he said. "The fact that they have not responded to Catherine Ashton is an important proliferation-related issue."
SANCTIONS CLOSE GAS FIELD
Ashton, the European Union's foreign policy chief, represents the P5+1 powers -- U.N. Security Council permanent members Russia, the United States, China, France and Britain, plus Germany -- and has invited Iran for talks in Vienna from November 15 to 17.
Iran has welcomed the offer of talks, which the powers want to yield a deal curbing its enrichment drive and opening it to U.N. nuclear inspectors in exchange for a package of benefits, but Tehran has yet to formally reply to the invitation.
"We are following up the issue," Mehmanparast said. "We should reach consensus on the venue and timing as well as the content of the talks."
Similar talks stalled a year ago, leading to the new U.N. sanctions and tighter U.S. and EU measures.
Ashton welcomed the news that a British gas field jointly owned by Iran and energy giant BP Plc was set to close due to the sanctions.
The Rhum gas field, 390 km (240 miles) off the northeast coast of Scotland had been under joint Anglo-Iranian control since 2003 and produced up to 6 million cubic meters of gas a day in the first six months of 2010, or about 1 percent of Britain's peak gas demand forecast for this winter.
Other European energy companies said they were considering whether to keep buying Iranian oil in 2011 due to sanctions.
While U.S. companies have long been prohibited from processing Iranian oil, firms elsewhere face no such ban. But traders say, since the sanctions, it is harder to pay for Iranian exports in currencies such as the euro and the dollar.
(Additional reporting by Hossein Jaseb and by Fredrik Dahl in Vienna, Conor Humphries in Moscow, Pete Harrison in Brussels, Louis Charbonneau and Patrick Worsnip at the United Nations, and Alex Lawler in London; Editing by Jon Boyle and Will Dunham)