A team of construction experts has arrived in Teheran to conduct a survey of Iranian requirements.

It includes a senior North Korean specialist in underground construction who helped design the bunkers that contain Pyongyang's illegal weapons program.

The talks center on whether the North Koreans will undertake the work for the Iranians, or act as advisers to Iranian construction companies.

The North Koreans specialize in the equipment and technology used in the construction of underground complexes.

In the past, the communist dictatorship has supplied tunnel-digging equipment for military purposes to Iraq, Syria and Libya.

The legal department of Iran's Revolutionary Guards, which is undertaking the project, summoned the managers of dozens of construction companies recently to discuss possible contracts.

The disclosure that Iran is continuing with its efforts to conceal details of its nuclear weapons program comes as the International Atomic Energy Agency, the United Nations-sponsored nuclear watchdog, prepares to publish later this week the latest report by its weapons inspectors into Iran's nuclear program.

``The Iranians are clearly feeling the heat over their attempts to build a nuclear bomb,'' said a senior Western intelligence official last week. ``They are desperate to keep the bomb-making part of their program secret.''

Iran insists it is interested only in developing peaceful nuclear energy, but US and British officials are convinced Teheran is working on a clandestine nuclear weapons project.

The Iranians were deeply embarrassed two years ago when traces of weapons grade uranium were found in soil samples taken from one of their nuclear research centers, prompting IAEA nuclear experts to intensify their investigation of Teheran's nuclear program.

The Iranians have long admired the North Koreans' ability to conceal their own nuclear weapons program, despite being under constant surveillance by US spy satellites.

Last week, in the most detailed discussion by the regime of its nuclear capabilities, Vice Foreign Minister Kim Gye Gwan told a US television channel Pyongyang had enough nuclear weapons to resist an attack by the US, and was building more. ``As for specifically how many we have, that is a secret.''

The Pentagon estimates North Korea has gathered enough material for at least six plutonium-based bombs since expelling IAEA inspectors more than two years ago.

US officials privately concede they still do not know their precise location. The Iranians tried to build their own underground facilities but these were quickly discovered by IAEA inspectors.

Now Teheran wants help to build a large new network of tunnels and caves at a secret location in central Iran.

According to Western intelligence reports, the first stage of the project would involve building 10,000 square meters of underground bunkers.

Each bunker would be divided into spaces of 1,000-2,500 square meters, big enough to house the equipment needed to produce weapons grade uranium.

In recent months, Teheran has engaged in a dangerous game of brinkmanship. Last week, it threatened to withdraw from talks with Britain, France and Germany - the so-called EU3 - on eliminating the more controversial aspects of its nuclear program, such as processing weapons grade uranium.

Iran agreed to suspend its enrichment program last year following detailed negotiations with the EU3, but provoked a diplomatic crisis last month when it threatened to continue its efforts to enrich uranium. Western intelligence officers believe the Iranians are trying to string out the EU3 talks to give themselves time to hide elements of the program that they do not want to declare.

Teheran has cooperated with North Korea on developing long-range ballistic missiles and bought a number of North Korean No-dong missiles, which were used to develop Iran's own Shahab-3 missile system.