THE UN atomic watchdog's top investigator yesterday begun talks with Iranian officials to press them to explain Western intelligence which suggested Iran had covertly studied how to design nuclear bombs.

Iran's official IRNA news agency said Olli Heinonen, who arrived in Tehran yesterday, met Javad Vaeedi, deputy head of the Islamic Republic's Supreme National Security Council, behind closed doors.

During his two-day trip, Heinonen will not visit Iran's Natanz underground uranium enrichment facility, the agency said.

Ali Asghar Soltanieh, Iran's representative at the International Atomic Energy Agency (IAEA), said Heinonen's visit was intended to advance cooperation between Iran and the IAEA, the UN body investigating Iran's disputed nuclear ambitions.

"Such talks ... display Iran's policy and determination to carry on its technical and expertise cooperation with the IAEA," Soltanieh told the semi-official Fars news agency.

Last week, US President George W Bush and British Prime Minister Gordon Brown pledged a united effort to prevent Iran from developing a nuclear bomb, possibly by expanding sanctions.

Iran says its nuclear programme is a peaceful drive to produce electricity so that the world's fourth-largest crude exporter can sell more of its oil and gas abroad. It has been hit by three rounds of limited UN sanctions since 2006 because of its inadequate cooperation with IAEA investigations.

Heinonen raised a diplomatic stir in February with a presentation that indicated links in Iran between projects to process uranium, test explosives and modify a missile cone in a way suitable for a nuclear warhead.

Iran has dismissed the intelligence as baseless, forged or irrelevant. Reuters