The Pakistan Government's acknowledgement that it is investigating some of its top nuclear scientists marks a significant departure from Islamabad's standard claim that its record on non-proliferation is "impeccable".
Doubts about Pakistan's non-proliferation record first emerged in the late 1990s when it became clear that Islamabad's Ghauri missiles, which have a range of up to 3,000km, were an improved version of North Korea's Nodong system.
The question was what Pakistan had given North Korea in
return for the missile technology.
There is widespread interest in Pakistan's nuclear know-how
The Ghauri missiles were developed at the Kahuta laboratories (recently renamed the Khan Research Laboratories), just outside Islamabad, under the guidance of the so-called father of the Pakistani bomb, Doctor A Q Khan.
Ever since 1974, when Islamabad decided it had to match Delhi's nuclear capability, Pakistan has had two, rival nuclear programmes. One has been run by the Pakistan Atomic Energy Agency (PAEC) and the other by Dr Khan.
After the fall of the Taliban regime in Afghanistan, there were more questions about Pakistan's non-proliferation record. Rumours circulated that retired Pakistani nuclear scientists had been living in Kabul, possibly helping Islamic extremists develop a dirty bomb.
Last year one retired scientist was taken in for questioning by the Pakistani authorities and later released.
In recent years American officials have discussed the possibility that Islamabad could be a proliferator. But either because of a lack of hard evidence, or a desire not to create problems for a key ally in the war on terror, the US has tended to play down its concerns.
Nevertheless, earlier this year, Washington did impose sanctions on the Khan Research Laboratories, citing concerns about missile technology transfers.
Reports in the US media that Pakistan may also have helped Iran and Libya develop nuclear technology has once again focused attention on the role of Dr Khan, a man who has always enjoyed financial and bureaucratic support from
While it is possible that some retired scientists went to work
in neighbouring Afghanistan on their own initiative, it is difficult to
imagine that Kahuta scientists would have been able to share nuclear technology with North Korea, Libya or Iran without the knowledge of some senior army officers.
If that did happen civilian leaders may well have been kept in the dark.
Two-time Pakistani Prime Minster, Benazir Bhutto, once complained that even when she was running the government she was unable to visit the Kahuta laboratories.
Suggestions that Libya and Pakistan have co-operated in the nuclear field go back many years. When he first decided that Pakistani should build a bomb there were claims that the then Prime Minister, Zulfikar Ali Bhutto, approached Libya for finance.
While there was never proof that any funds were provided, there was speculation at the time that Libya would not
provide funds without expecting something in return.
Other countries have expressed an interest in Pakistan's nuclear know-how.
In August 1999, - the year after India and then Pakistan declared themselves as nuclear powers - the Saudi Crown Prince and Defence Minister, Sultan Bin Abdul Aziz, visited Kahuta amid such secrecy that a Pakistani spokesman at the time denied the minister had ever been there.
And in May 2000 an Urdu language Pakistani newspaper reported that the Information Minister of the United Arab Emirates had also visited Kahuta.