Iran is working on nuclear fusion and "competing" with international efforts to harness the technology, an Iranian nuclear official told state television Monday.

"The first test of nuclear fusion was done five years ago. Iranian nuclear scientists are competing with the modern world in the field of the production of nuclear energy by nuclear fusion," said Sadat Hosseini, head of engineering in Iran's Atomic Energy Organisation.

However an informed source in the organisation played down the importance of his comments, asserting that work was still at the "research level".

"Different tests of fusion have been done at a research level for years in the research centre of Amirabad in Tehran, and it's nothing new," said the source.

Nuclear fusion is touted as the cheap, safe, clean and almost limitless energy source of the future. In fusion, atomic nuclei are fused together to release energy, as opposed to fission — the technique used for nuclear power and atomic bombs — where nuclei are split.

Iran insists that its nuclear programme is only directed at meeting future energy needs, but is currently under mounting international pressure to halt activities seen as a cover for weapons development.