WASHINGTON, Aug 7: US Vice-President Dick Cheney has said that the presence of a network of nuclear proliferators in Pakistan was one of the major problems the Bush administration had to tackle.

Mr Cheney's remarks, delivered at a Friday evening election rally in Minnesota, come amid increased efforts by some US lawmakers to re-impose strict economic sanctions on Pakistan over the nuclear issue.

"We knew, through intelligence sources, that a man named A.Q. Khan, who had developed the Pakistan nuclear weapons programme, after he'd finished that work for Pakistan, had then gone into business for himself," said Mr Cheney.

"He was selling nuclear weapons technology to some of the worst regimes in the world - the North Koreans, the Iranians, and the Libyans, in particular. Moammer Qadhafi, in Libya, was one of his best customers," he said.

The US vice president said that Dr Khan, who manufactured centrifuges needed to enrich uranium to the weapons grade, later sold these equipment to the countries that are considered rogue states in Washington.

Although the Bush administration supported Pakistan when Dr Khan acknowledged exporting nuclear technology to Iran, Libya and North Korea, the dispute is rapidly becoming an election issue in the United States.

Earlier this week, the US House of Representatives has referred to its committee on international relations a new bill that seeks to put Pakistan in a straitjacket on the pretext of rolling back the effects of the A.Q. Khan network.

The nuclear Black Market Elimination Act, introduced in the House by Rep Tom Lantos earlier this week, "seeks to impose sanctions on foreign entities that engage in certain nuclear proliferation activities."

The proposed law specifically calls for sanctions against Pakistan, if it fails to get a clean chit from the US president on the nuclear issue.

The proposed bill says that before providing any assistance to Islamabad in future, the US President must make sure that Pakistan is fully sharing all information pertaining to A Q Khan's proliferation network, besides providing full access to the scientist and his associates.

It requires the US president to certify to the appropriate congressional committees that Pakistan has verifiably halted any cooperation with any state in the development of nuclear or missile technology. He will also certify that Pakistan is not providing any material, or equipment, or any other technology, material, or equipment that is useful for the development of weapons of mass destruction, including exports of such technology, material, or equipment.

Not later than 30 days after the enactment of this act, the US President shall submit a report to the appropriate congressional committees, identifying any country that might have benefited from the Khan network.