Iran's first nuclear power plant, which Russia is building in the town of Bushehr, will not be completed before 2008, Russia's top nuclear official said Wednesday.

Tehran's hope that the plant will launch this year is "unrealistic," said Sergei Kiriyenko, head of federal nuclear agency Rosatom, quoted by Russian news agency ITAR-TASS in the Uzbek capital Tashkent.

"It's perfectly clear... that the launch can happen no earlier than 2008."

Washington has consistently pressed Moscow not to launch the Bushehr power station, which it fears could cover weapons-related work, while Tehran insists its only goal is electricity generation.

Kiriyenko said the latest hold-up to the project was a result of Iran falling behind on payments and delays in shipping parts for the plant from third countries.