Pakistan's government has detained two nuclear scientists with close ties to the Taleban rulers of Afghanistan. Pakistani officials say the two are being questioned in connection with their pro-Taleban activities, and not with anything having to do with their work on nuclear-related issues. The case of the two nuclear scientists has raised questions about nuclear safety in the region.

For more than one week, nothing has been heard from the two scientists, Bashiruddin Mehmood and C.A. Khan.

Of the two, Bashiruddin Mehmood is the better known. For years he played a prominent role in Pakistan's nuclear program, only to resign just over two years ago after he bitterly protested then-Prime Minister Nawaz's Sharif's proposed intention to sign the Comprehensive Nuclear Test Ban Treaty (CTBT), which bans all testing of nuclear weapons. Pakistan and India both tested nuclear devices in 1998 but have yet to sign the CTBT.

C.A. Khan is less well known, but both men have become closely identified in Pakistan with raising money to help the Taleban.

Pakistan's presidential spokesman, Major General Rashid Qureshi, says it was their pro-Taleban activities and not their nuclear know-how that resulted in both men being taken in for questioning.

"I want to clarify here that ... neither of them had [anything] to do with the weapons program," he said. "That fear that they were weapons-related is not correct at all. As to what questions were asked of them, they were running an NGO," he said. "There have been over the last few months efforts to identify people who were running NGOs and have them registered according to rules and laws. There were also questions as to their reasons for visiting Afghanistan," he said.

Pervez Hoodbhoy is a professor of physics at Quaid-i-Azam University in Islamabad who has studied the nuclear weapons programs in both Pakistan and India. He says Pakistan has pursued two strategies in recent years in developing nuclear weapons - one involving the processing of enriched uranium, and the other involving the processing of plutonium.

Professor Hoodbhoy said that until recently, Bashiruddin Mehmood probably knew more about making plutonium-based nuclear bombs than anyone else in Pakistan.

"Until the CTBT issue came to the fore, Bashiruddin Mehmood was the head of the Kushaab reactor. The Kushaab reactor has one single purpose, which is that of producing weapons-grade plutonium," Professor Hoodbhoy said.

Pervez Hoodbhoy says until Bashiruddin Mehmood resigned, he was intimately involved with the production of nuclear weapons in Pakistan. Islamabad is believed to possess enough fissionable material to construct about 30 nuclear bombs.

Pervez Hoodbhoy has said given Bashiruddin Mehmood's extensive knowledge about how to build nuclear weapons, his frequent travels to Afghanistan should be a cause for concern.

"I would certainly be concerned because his sympathies are very much with the Taleban, and he has been going on around the country and openly preaching the Taleban message and saying what they are doing is fine and it is only the western propaganda which is being used to discredit the Taleban, and so forth," he said. "At the same time, he has very deep links and connections with those in the nuclear business within Pakistan. So yes, I would be worried, but I am not suddenly worried about this. I think this has been a cause of worry for a decade or so and nuclear weapons in Pakistan and in India are inherently a source of instability, and one day we are going to see the consequences," he said.

Pakistani newspapers say investigators looking into the activities of Bashiruddin Mehmood and C.A. Khan are also looking into the activities of some of their former colleagues who still work in Pakistan's nuclear program.

Pervez Hoodbhoy has said there is widespread discontent in Pakistan's nuclear laboratories over the current U.S. campaign against terrorist and military-related targets in Afghanistan.

"Within the nuclear establishment you will find a great deal of anti-Americanism, rightly or wrongly. There is a lot of resentment against the United States and this is going to grow as the bombing of Afghanistan continues," he said. "What this will cause individuals within that establishment to do I think is a matter of speculation, but yes, I do believe that there are serious dangers here," he said.

Pervez Hoodbhoy says nuclear weapons can be spread by transferring actual bombs or the cores of those bombs, which he says is extremely unlikely, or by the transfer of small amounts of weapons-grade material, such as enriched uranium. But the Pakistani nuclear scientist says the most valuable asset in building a nuclear weapon is hands-on experience, and that he says, should be a cause for concern in the case of Bashriddun Mehmood and C.A. Khan.