Sultan Bashiruddin Mehmood and Abdul Majeed, both scientists who had retired from the Pakistan Atomic Energy Commission (PAEC), were picked up after the FBI provided evidence of their links to jehadi outfits.

The Pakistan Interior Minister, Moinuddin Haidar, said on Thursday that Bashiruddin was being taken into "protective custody." Military spokesman, Rashid Qureshi, only said the scientist was being questioned.

After retirement, Bashiruddin had formed an NGO called Ummah Tameer-e-Nau (Reconstruction of the Muslim Ummah). This NGO was affiliated to the Al Rasheed Trust, an organisation banned for its links with Al-Qaeda network. The NGO was one of the few allowed by Mullah Muhammad Omar to carry out relief work in Afghanistan.

Majeed was the chief engineer of PAEC until last year. Pakistani press reports said he had been trying to get a hold of supplies of plutonium and enriched uranium to send to the Taliban.

Bashiruddin was with the PAEC for 35 years. He held many senior positions, including director of the Kahuta Enrichment Project. He was also one of the designers of the Khusab nuclear plant in Punjab. He took early retirement in 1998 to protest moves by the then Nawaz Sharif government to sign the CTBT, a treaty he strongly opposed.

Bashiruddin founded Ummah Tameer-e-Nau after vowing to rebuild Afghanistan. Most of its membership consisted of nuclear scientists and military officers. Bashiruddin's Islamic fervour was well known, catching even the attention of Mullah Omar.

The Taliban gave him permission to conclude business agreements on their behalf. This strengthened suspicions that Bashiruddin's NGO was looking for nuclear hardware for Kabul.

He and Majeed had been under investigation by a joint US-Pakistani intelligence team.

The West is reportedly also concerned about A.Q. Khan, the father of Pakistan's nuclear bomb. Khan resigned as head of the country's nuclear programme in March this year. Because he had publicly expressed sympathy for the jehad movement, it was rumoured he was joining the fundamentalists.

The detention of the two scientists follows statements by Pakistani officials, including President Pervez Musharraf, that the country's nuclear installations and assets were secure.

There have been persistent rumours Bin Laden has sought weapons of mass destruction —chemical, biological and nuclear.

Pakistan is increasingly seen as a possible source of such weaponry for the Taliban or Bin Laden. One reason is the large number of scientists employed by its nuclear programme. The other is the creeping popularity of the fundamentalist cause among educated, urban Pakistanis.

In the past, the most likely source was one of the "loose nukes" scattered about the ex-Soviet Union. Seven years ago, Russian agents stopped a planeload of Russian nuclear scientists heading off to North Korea.

Says Michael Krepon of the Henry Stimson Centre in Washington, which does research on nuclear security, "It is easy to get fissionable material, but difficult to make a bomb." He points out the Taliban could just mix nuclear material with RDX. This would not produce an atomic explosion. But, say other experts, the very knowledge Kabul has weapons-grade nuclear material could deter US bombing as Washington would have to fear a terrorist strike that could leave nuclear contaminants.