Iran began loading uranium fuel rods into the core of its first nuclear power plant on Tuesday, a process considered as the last major step to start up the long-delayed Russia-built reactor.

Head of the Atomic Energy Organization of Iran Ali-Akbar Salehi said "injecting 163 fuel rods into the core of the Bushehr reactor has started," and the plant would join national grid in mid-February, the semi-official ISNA news agency reported.

"Although it is an approximate date, we hope that if everything goes according to the schedule, we could see the plant connected to the national grid in mid-February," Salehi said.

Officials said the fuelling of the Bushehr plant termed by Salehi as "one of the most sensitive nuclear power plants in the world" showed Iran's nuclear drive was on track despite sanctions aimed at curbing its uranium enrichment, a major concern for the West.

Yukiya Amano, chief of the International Atomic Energy Agency (IAEA), called on Iran to address concerns about its nuclear aims.

"I am requesting Iran to take concrete steps, concrete measures toward the full implementation of their obligations," he said in Moscow.

U.S. Secretary of State Hillary Clinton said on Tuesday that Iran is entitled to the peaceful use of civilian nuclear power, but not to nuclear weapons.

Washington has no problem with the Bushehr plant, she told reporters at a meeting with Austrian Foreign Minister Michael Spindelegger.

"Our problem is not with their reactor at Bushehr, 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," she said.

Clinton also voiced Washington's hope to see Tehran back to the negotiating table with the United States, Britain, France, Germany, Russia and China, on a package of incentives in exchange for Iran halting enrichment.

On Thursday, European Union (EU) foreign policy chief Catherine Ashton proposed a new round of talks with Iran in Vienna in mid-November with the participation of the United States, Britain, China, France, Russia and Germany.

Iranian Foreign Minister Manouchehr Mottaki welcomed the EU offer on Friday, saying that "we are hopeful that through exchange of views by both parties, we would come to an agreement regarding the date, venue and more important content and agenda of this negotiation."

Western countries have repeatedly called on Tehran to halt its sensitive nuclear program but Iran insists on the civilian purposes of its nuclear activities.

Similar negotiations over Iran's controversial nuclear program stumbled a year ago, leading to the fourth round of UN sanctions.

In July, following the UN and U.S. sanctions against Iran, the EU also endorsed tougher sanctions against Iran over its nuclear program, including measures to block oil and gas investment and curtail its refining and natural gas capability.

Amid nationwide celebrations, fuel rods were delivered to the first unit of the 1,000-megawatt Bushehr nuclear power plant in southern Iran in August, but they were not inserted into its core due to what were described as minor technical problems.

The Bushehr nuclear plant has been beset by decades of delay. Its construction was started in the 1970s by a German company but was shelved shortly after the Islamic Revolution in Iran in 1979 as the German side pulled out of the deal.

Russia signed an agreement worth 1 billion U.S. dollars in 1995 to take over the project. Its completion, first scheduled for 1999, was postponed several times by mounting technological and financial challenges and interruptions under pressures from the United States.

Under a deal between Moscow and Tehran in 2005, Russia will provide nuclear fuel for Iran and take back all spent reactor fuel, and experts of the IAEA will be able to verify that no fuel or waste is diverted elsewhere.