The head of the UN's nuclear watchdog arrived in Tehran early today for 24 hours of talks he hopes will convince the Islamic republic's to open up its suspect nuclear programme to more rigorous inspections.

International Atomic Energy Agency (IAEA) director general Mohamed ElBaradei wants Iran to immediately and unconditionally sign, ratify and implement an additional protocol to the nuclear Non-Proliferation Treaty (NPT).

That would grant his inspection teams the power to make surprise visits to suspect facilities.

At present, Iran is only obliged to accept pre-arranged visits to sites it chooses to declare.

Official sources said ElBaradei was to spend much of the morning in talks on the thorny issue with Iran's atomic energy chief and Vice President Gholam-Reza Aghazadeh.

He is also due to meet Iran's reformist President Mohammad Khatami and Foreign Minister Kamal Kharazi.

Although natural resource-rich Iran has fiercely denied US allegations that its atomic energy programme is merely a cover for a top-secret bid to acquire nuclear weapons, officials are so far showing no sign of buckling to the international demands.

ElBaradei is expected to be told by Iranian officials that they see demands for more inspections as being driven by old arch-enemy the US, and that while they have nothing to hide, their signing of the protocol can only come after lengthy talks that would bring an end to what they see as unfair treatment.

According to the terms of the NPT, signatories are obliged to provide mutual assistance in peaceful nuclear technology. Only Russia is helping Iran's power project near the southern city of Bushehr.

ElBaradei will also be holding follow up talks to his June report to the IAEA board of governors, in which he said Tehran had not fully respected the NPT by failing to inform the IAEA of some of its nuclear activities, including the import of uranium in 1991. - Sapa-AFP.