The Bushehr nuclear plant in southern Iran is normally shrouded in secrecy. But ABC News and other journalists were today granted unprecedented access to the site, which is currently under construction.
The plant is surrounded on all sides by early warning radar and anti-aircraft guns. There are two reactors at Bushehr -- reactor No. 1 is nearing completion and about to come online.
The Bushehr plant was designed and is being built by Russia. Some of the Russian engineers supervising construction told ABC News it was similar to some U.S. reactors.
The plant's nuclear fuel has already been made in Russia and is ready for delivery, officials say. Iranian officials say it will probably arrive in the country and be placed in the reactor's cylinder before the end of the year.
The Bush administration strongly believes that Iran may be trying to build a nuclear weapon. The Iranians, who have vast reserves of oil and gas, say they need a nuclear program as a peaceful source of energy.
Iran has agreed to send all used nuclear fuel back to Russia, which would eliminate the ability to reprocess the fuel to make nuclear weapons.
"Bushehr is totally under the safeguard regime of the IAEA," said Asadollah Saboury, vice president of the Atomic Energy Organization of Iran.
The International Atomic Energy Agency has visited the site several times and plans to install cameras to help ensure that Iran is not using the plant for a weapons program.
Today, however, Iranian officials said the country maintains the right to make its own nuclear fuel.
Iran insists the plant is purely for civilian use and that the country needs the power that will be generated by Bushehr's massive turbines.
U.S. officials said today's tour and statement from the Iranians do not change the fundamental problem.
"Our concern is that Iran is pursuing a nuclear weapons program under the cover of a civilian program. That remains a concern," said White House press secretary Scott McClellan in a news conference.
When the Bushehr plant starts functioning, experts say it could produce enough plutonium to make dozens of nuclear bombs.
Although Iran has allowed some inspections, the United States wants full access for international monitors -- including unscheduled, unannounced visits at all suspected nuclear fuel facilities across the country.
For 18 years, Iran kept its uranium enrichment program secret from the world. It was finally exposed by an Iranian opposition group in 2002.
Iran has since allowed some inspections. IAEA tests have revealed some inconsistencies in Iran's claims, but no hard evidence of a nuclear weapons program.
ABC News' Jim Sciutto and Bob Woodruff filed this report for "World News Tonight."