A United States Congressional panel took the Bush Administration to task for not doing enough to pressurise Pakistan to unravel the depths of the damage caused by the AQ Khan nuclear network.

At a hearing of the Subcommittee on International Terrorism and Nonproliferation in Washington on Thursday, its Republican chairman Ed Royce of California set the tone for the deliberations saying Khan's network has done ''incalculable and potentially catastrophic damage'' to international security.

It said the network has opened an era in which many states, including among the unstable and most hostile to the United States, can now expect to develop nuclear weapons. ''This is Khan's grim legacy,'' he added.

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The hearing brought out the grave danger of how the network may have helped Al Qaeda [Images] and other terrorist groups to obtain nuclear secrets and the possibility of radical Islamists seizing control of Pakistan's government and its nuclear arsenal.

Describing the AQ Khan network as the 'Wal-Mart of private sector proliferation', Royce said its handiwork has helped deliver two of the most threatening security challenges that the United States faces today -- North Korea and Iran.

It ran for over a decade a sophisticated and multinational clandestine network, built around Pakistan's own nuclear weapons programme that passed on nuke enrichment technology to hostile countries, as well as to Libya.

''US policy rightly attempts to work with and pressure the Pakistan government on counter-terrorism, proliferation and other concerns, but not to a destabilising degree,'' he said.

Royce and the ranking Democrat on the Subcommittee Brad Sherman from California and Gary Ackerman from New York said the AQ Khan network is far from closed.

They said the Bush administration has soft-pedaled the issue for too long while Pakistan has provided little information on the network which has caused enormous damage to stop the spread of nuclear weapons, to US national security and to international peace and stability.

The Congressmen also regretted that the international response thus far has not been sufficiently effective.

Although revelations about the Khan network have re-energised support for a range of reforms, more extensive improvements to the international nonproliferation regime are still needed to block the emergence of new networks and to detect them promptly if they do arise, they said.