"Iranian nuclear scientists are trying to catch up the advanced world in using nuclear energy through nuclear fusion," Sadat Hosseini, who runs the technical department at the Nuclear Research Center of Iran's Atomic Energy Organization, was quoted as saying.

"Iranian scientists have firstly tried nuclear fusion five years ago," he added.

Through nuclear fusion, multiple nuclei join together to form a heavier nucleus.

The process of nuclear fusion is accompanied by the release or absorption of energy depending on the masses of the nuclei involved.

Nuclear fusion is employed by certain kinds of atomic bomb. The announcement came during a current visit of Russian Security Council Secretary Igor Ivanov for talks with senior Iranian officials on its disputed nuclear issue.

Tehran is under intense international pressure to stop its uranium enrichment and the United States accuses Iran of using its civilian nuclear program as a cover to achieve an atomic bomb. Iran denied the charge and insisted its nuclear program is only for peaceful use.

The five permanent members of the UN Security Council plus Germany are expected to have more talks on a decision to offer Iran a package of incentives in return for Iran's suspension of its nuclear activities, after their London talks on May 24 stopped short of making a final agreement.

Foreign ministers of the six nations were likely to meet on Thursday in the Austrian capital of Vienna to discuss the matter.