The United States will press Pakistan to tighten nuclear export controls to prevent any future black market proliferation networks, Christina Rocca, the assistant secretary of state for South Asian affairs, told a congressional hearing.

Opposition Democratic legislators had demanded that the government tie aid to Pakistan with progress it makes on nonproliferation, anti-terrorism cooperation and democratization.

Rocca said Pakistan's nuclear program remained under scrutiny four months after it was linked to a proliferation network led by Abdul Qadeer Khan, the father of the country's nuclear bomb who publicly confessed to selling nuclear secrets to Iran, Libya and North Korea.

Gary Ackerman, the Democratic representative from New York, asked Rocca at the hearing whether the government continued to ask Pakistan for information on the illicit network or whether the investigation had been completed.

"Oh, no, it continues," she said. "It continues, and we're working very closely with the government of Pakistan on the investigation."

Rocca said Washington had to rely on information provided by Pakistani authorities on the network's activities, having had no access to Khan, who has been pardoned by President Pervez Musharraf.

She said she could not answer whether the government had asked to interview the scientist, pointing out that it was an "extremely sensitive matter."

Ackerman and another Democratic legislator, American Samoa Representative Eni Faleomavaega, suggested that conditions be imposed on a five-year, three-billion-dollar aid package to Pakistan beginning in fiscal year 2005 to ensure that it kept its word.

"I believe the time for conditions is now," Faleomavaega said. "And I would like to clearly state that I do not believe we will see an end to terrorism or nuclear proliferation until the US Congress imposes restrictions on US aid to Pakistan."

Rocca insisted that the United States had very close cooperation with Pakistan on non-proliferation, anti-terrorism cooperation and democratization.

"We don't see any reason -- there has been no cause at all for us to have second thoughts about providing any assistance to Pakistan," she added.

Ackerman felt the Bush administration had struck a very bad bargain with Pakistan by "giving a pass on nuclear proliferation issues" in exchange for perceived cooperation in the war on terrorism.

He questioned military ruler Musharraf's seriousness in battling terrorism and embracing democratic reforms as well as the level of support he received among moderate Pakistanis.

"We are hitching our wagon to a very questionable horse," he said.

Rocca said the United States was working relentlessly with Pakistan to increase and tighten its nuclear weapons exports control regimes.

Pakistan recently introduced a bill in parliament which, if passed, "would go a long way to towards meeting the standards that we are encouraging them to reach," she said.

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