BUSHEHR, Iran -- Iran's first nuclear power plant, which the United States claims can be used to make nuclear bombs, is nearing completion and all major components are installed, Iranian officials said Tuesday.

"Over 70 percent of the work has been accomplished," Assadollah Sabori, deputy head of Atomic Energy Organization of Iran said in a press conference. "The main thing left is shipping nuclear fuel from Russia, which is expected to take place in May," he said.

The United States has accused Iran of seeking to develop nuclear weapons and says the plant will be able to produce nuclear material for a bomb. Iran says the plant will be used to meet the country's growing electricity needs.

Sabori spoke after more than 80 international journalists and photographers toured the facility in southern Iran for the first time Tuesday.

Steam generators, pressure vessels, pressurizers and reactor cooling plants have already been installed. The components, shipped to Iran from Russia in the past 18 months, form the core of a nuclear reactor.

Sabori said 1,100 Russian experts and over 3,000 Iranians are working at the plant's first unit. He said Iran had the option of setting up three other reactors at Bushehr, 745 miles southwest of the capital Tehran.

He said Iran has agreed to return the spent nuclear fuel to Russia but that some formalities remained before Iran makes the deal official.

Iran says the 1,000-megawatt Bushehr plant is part of efforts to supply enough electricity to its 66 million people. Iran has approved a plan to produce 6,000 megawatts of power through nuclear energy by 2020.

On Monday, the White House challenged Iran's claims that it was building the plant strictly for energy production.

"We completely reject Iran's claim that it is doing so for peaceful purposes," White House spokesman Ari Fleischer said. State Department spokesman Richard Boucher called Iran's nuclear weapons program robust.

But Naser Shariflou, head of Bushehr, denied that Tuesday. "Simply, it is impossible to make a bomb with a plant like this," he said.

Shariflou said the International Atomic Energy Organization has already installed equipment including cameras to monitor the plant's activity.

"Everything will be under the direct supervision of the IAEA. Even the spent nuclear fuel will be watched closely by IAEA cameras here before it is shipped to Russia," he said.

David Albright, head of the Institute for Science and International Security in Washington and a former weapons inspector in Iraq, told the AP Tuesday that Bushehr can be used to produce weapon-grade plutonium.

"Plutonium with a high fraction of plutonium 240, commonly called reactor-grade plutonium, can be used to make a crude nuclear explosive. Moreover, Bushehr could be used to produce weapon-grade plutonium directly," Albright said.

He said a uranium enrichment plant under construction at Natanz, in central Iran, was a gas centrifuge plant that can make either low enriched or highly enriched uranium; the latter is used in a nuclear weapon. IAEA inspectors visited Natanz last month.

Rasul Sediqi, an Iranian nuclear scientist, said the plutonium obtained from the Bushehr plant will be of no use for nuclear weapons.

"The plutonium obtained consists of plutonium 239 and 240. And it's extremely difficult to separate them because Iran doesn't have such an advanced technology to do so," Sediqi told The Associated Press.

Plutonium 239 is the weapons-grade plutonium used in nuclear weapons.

American analysts, however, said it is possible to make weapons out of material that contains 240, "as long as it is not too high a percentage," said Joseph Cirincione, of the Carnegie Endowment for International Peace. "This provides Iran with a source of weapons material, if they have the facility to reprocess the fuel and separate the plutonium."