The warning came as details emerged of how disgraced one-time hero Abdul Qadeer Khan ran a shady underworld network from Dubai with contacts in three continents, trading in nuclear centrifuges and atomic bomb blueprints.

But despite receiving a presidential pardon from President Pervez Musharraf on Thursday after admitting to handing over atomic data to Iran, Libya and North Korea, Khan will remain under tight security, unable to move around at will.

"It is a conditional pardon and Khan knows he would be jailed if he tries to proliferate again in any way," a senior government official involved with the investigation into the scandal told AFP.

The proliferation saga stretches back over two decades.

Officials said Khan was protected against any demand for his handover from a foreign country or agency after authorities registered a police dossier against the tall, greying scientist for offences under the official secret act.

"The measures provide a protected wall around the fallen hero," one said.

According to government insiders, Khan ran a black-market network from the Middle East trading in centrifuges for uranium enrichment.

"During the last 48 months, Dr. Khan made as many as 44 foreign trips to Dubai and separately also to Malaysia, Libya and Iran," a government official told AFP on Friday, speaking on condition of anonymity.

The 68-year-old former metallurgist used his experience working with a European nuclear agency in the 1970s to enable Pakistan to build centrifuges to enrich uranium and build a nuclear bomb.

Dubai was the springboard for his proliferation activities where centrifuges secretly built in Malaysia by a pseudo-commercial firm were brought and then passed to end users, the government official said.

"When he was in Malaysia last year we summoned him back for fears that he might be picked up by some foreign agency," he added.

Another detained Pakistani nuclear scientist, doctor Mohammad Farooq, formed the core of the proliferation network which also included individuals from South Africa, Germany, Holland, Sri Lanka, Malaysia and Dubai, he said.

Farooq was the first scientist brought in when officials launched a probe last December, after being alerted that Pakistani nuclear secrets were being traded abroad.

Farooq was asked at one stage by Khan to get himself and another nuclear scientist doctor Nazir Ahmed a job with the Malaysian firm producing centrifuges in order to make the clandestine operations easier, the government official said.

An analyst said Pakistan could face pressure from abroad to make Khan available for questioning.

"If he emerges as lord of the proliferation ring, Pakistan will face an increased pressure to give the international community access to this guy for questioning," Quaid-e-Azam University's strategic studies department head Riffat Hussain told AFP.

"That can pose a difficult situation for Musharraf."

Khan's downfall has shocked Pakistan, where he was regarded as a hero for developing the country's nuclear programme.

Islamic party supporters called a nationwide strike Friday to protest the "humiliation of national heroes", including five scientists and administrators from Pakistan's main uranium enrichment facility who were formally arrested Wednesday.

The five had been detained for weeks as part of the investigation into the nuclear leaks.

Protesters enforcing the strike burnt tyres and stoned cars in the southern port city of Karachi, where minor scuffles between youths and police left three people injured, witnesses said.

Police said they had arrested 50 people during "incidents of minor violence".

A complete strike was observed in the central city of Multan and some nearby cities, but the shut down was only partial in other cities and completely ignored in cities such as Lahore and Islamabad, residents said.

WAR.WIRE