Pakistan was the source of the centrifuge design technology that made it possible for Libya to take major strides in the last two years in enriching uranium for use in nuclear weapons, US officials and other Western experts have said.

"These guys are now three for three as supplier to the biggest proliferation problems we have," a senior official in Washington told The New York Times, referring to previously reported Pakistani aid to the nuclear programmes of North Korea and Iran.

Bush administration officials emphasised that they possessed no evidence that the government of President Pervez Musharraf knew about transfer of technology to Libya, which helped finance Pakistan's early nuclear weapons programme three decades ago, The Times reported.

But the timing of the transfer of the centrifuge design from Pakistan, the paper said, calls into question Musharraf's ability to make good on his vow to US President George W Bush that he would rein in Pakistani scientists selling their nuclear expertise around the globe.

The general made that pledge shortly after the September 11, 2001, terror attacks in the United States. Yet the main aid to Libya appears to have gone to Libya since those attacks, suggesting that Pakistani scientists may have continued their trade even after the explicit warning, the paper said.

"It has all the hallmarks of a Pakistani system," the senior US official said.