Secretary of State Colin Powell was unwilling to publicly confirm or deny a report that designs for a Pakistani centrifuge had helped Libya take major steps forward in its nuclear program within the last two years.

"I don't have enough information at hand to answer a question quite as specific as that," Powell told reporters at the State Department.

"We know that there have been cases where individuals in Pakistan have worked in these areas and we have called it to the attention of the Pakistanis in the past.

"I'm very pleased now that President Musharraf is aggressively moving to investigate all of that."

Pakistani authorities last month took in Farooq Mohammad and Yasin Chohan, directors of Pakistan's key uranium enrichment facility Kahuta Research Laboratories (KRL), for questioning.

A government spokesman said the father of the country's nuclear programme and former KRL chairman, Abdul Qadeer Khan, had also been questioned.

The White House earlier also made clear that it did not view the report as proof that Musharraf was not living up to his pledge to halt Pakistani proliferation activities.

"We fully expect President Musharraf and the government of Pakistan to follow through on those assurances," spokesman Scott McClellan said.

But he added: "We recognize that it's always difficult to control the activities of rogue individuals whose motives are personal gain."

Musharraf has been a key ally in the US campaign against terrorism in South Asia, and there has been intense concern in Washington for his safety, after he narrowly escaped a pair of recent assassination attempts.

The New York Times quoted US officials in Washington and other Western experts as saying they had no evidence that Musharraf's government -- which vowed after the September 11, 2001 attacks that such transfers have stopped -- knew about the episode.

But it reported that the "main aid to Libya appears to have come since those attacks, suggesting that Pakistani scientists may have continued their trade even after the explicit warning."

Many of the centrifuge parts that Libya imported were manufactured in Malaysia, the paper said, quoting unnamed experts familiar with the investigation.

The transfer of Pakistani designs made it possible for Libya to make "major strides" in enriching uranium for use in nuclear weapons, the paper said, quoting unnamed Bush administration officials and other Western experts in a report datelined Tripoli.

"These guys are now three for three as supplier to the biggest proliferation problems we have," the Times quoted a senior official in Washington as saying, referring to alleged Pakistani help for North Korea's and Iran's nuclear programs.

US and Western experts are gleaning new information about Libya's nuclear program and how it was supplied after Tripoli's surprise announcement on December 19 that it would dismantle its weapons of mass destruction programs and allow international inspections of its nuclear facilities.

The United States said publicly just last month that it believed Pakistan's vows not to shop nuclear secrets around the world, following allegations it had helped involved in Iran's quest for weapons of mass destruction.

State Department spokesman Richard Boucher referred reporters to remarks made by Secretary of State Colin Powell in October 2002, after he addressed the matter with Pakistani President Pervez Musharraf.

"He assured us that Pakistan was not participating in any kind of activity of that nature, and I checked this morning and I would say that we continue to accept that assurance," said Boucher on December 22.

Powell and aides have pointedly not ruled out previous nuclear transgressions by Pakistan.

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