WASHINGTON (Reuters) - The CIA had some knowledge of Pakistani nuclear scientist A.Q. Khan's proliferation activities while they were in progress but did not pay enough attention to them, a London-based researcher said Tuesday.

"There's no doubt that the CIA knew about some of Khan's activities at various stages of his proliferation" operation, said Mark Fitzpatrick, a former top U.S. non-proliferation official now with the International Institute of Strategic Studies think tank.

"There's also no doubt that the CIA didn't give enough attention to this area of private sector proliferation in looking at Iran's nuclear development program over the years" because like other western intelligence agencies, it was more focused on state to state activities, he said.

Fitzpatrick, briefing journalists on a new IISS report on Khan and nuclear black markets, added, however, that the report did not thoroughly examine or draw firm conclusions on the extent of the CIA's knowledge.

In response, CIA spokesman Paul Gimigliano said: "The disruption of A.Q. Khan's proliferation network was a major success, one in which the CIA played a crucial role. To suggest otherwise is to ignore the facts.

"As with so many other intelligence triumphs, this was the result of hard, careful, essential work over time," he added.

BLACK MARKET BUSINESS

Khan, an admired figure in Pakistan, was arrested in January 2004 for his central role in the black market that sold Pakistani nuclear weapons technology to Iran, North Korea and Libya and offered technology to Iraq and perhaps other countries.

Although officially pardoned by President Pervez Musharraf, Khan remains under house arrest.

After Pakistan acted against Khan, President Bush declared that the network had been shut down.

But the IISS report said that "at least some of Khan's associates appear to have escaped law enforcement attention and could, after a period of lying low, resume their black market business."

It also concluded that "the few prosecutions and light sentences that have been imposed to date (on Khan and his accomplices) are not commensurate with the scale of the proliferation that the Khan network abetted."

Pakistan has insisted the network was the work on one man -- Khan -- and his associates. While this argument "cannot be taken at face value ... neither is there validity to the claim that Khan was a front, doing the government's bidding in each of these cases," the report said.