United States Secretary of State Hillary Clinton [Images] has expressed concern over the release of Pakistan's disgraced scientist A Q Khan from house arrest.

"I am very much concerned," Clinton told media persons in response to a question on the issue during a joint media availability with Philippine President Macapagal-Arroyo, at the Foggy Bottom headquarters of the State Department in Washington.

"We'll have more to say about that," Clinton said in her brief response about the decision by a Pakistani court to free Khan.

Earlier in the day, the State Department, however, made it clear that it is not pleased with the release of the "father" of Pakistan's nuclear programme from house arrest.

The state department spokesperson, Gordon Duguid said, "The US believes that Khan continues to be a significant proliferation risk and it would be unfortunate if he were to be released from house arrest."

"The proliferation support that Khan and his associates provided to Iran and North Korea has had a harmful impact on the international security," Duguid added.

Meanwhile, a key US lawmaker has cautioned that Islamabad's [Images] move to release A Q Khan could have an adverse impact on American aid to Pakistan.

"Congress will take this into account as we review and create legislation on the US-Pakistan relations and the circumstances under which US assistance is provided to Islamabad," Congressman Howard Berman said after a Pakistani court ordered the release of Khan from house arrest.

Berman is the chairman of the House Committee of Foreign Relations, the powerful Congressional committee that plays a key role in shaping US foreign policy.

In the coming weeks, the House of Representatives and the Senate are likely to take up a legislation, which proposes to triple the non-military aid to Pakistan amounting to $1.5 billion per annum for the next ten years.

Berman alleged that the US officials have been prevented from interviewing Khan to try to determine the extent of the damage he has done to the world stability.

"It is very alarming that A Q Khan, the worst proliferator of nuclear weapons technology in history, has been freed," Berman said in a statement.

"It is unclear whether the illicit smuggling network he created was fully dismantled, even after he was placed under a nominal house arrest," Berman added.