WASHINGTON - The United States is keeping a close watch on the network of Pakistani scientist A.Q. Khan, a State Department spokesman said after an American newspaper raked up the issue again. "While A Q Khan himself is out of business, according to the Government of Pakistan, we watch his network very closely for signs that others within his realm are still in business," Spokesman P J Crowley told reporters at the regular news briefing. Responding to questions, he said that it was an ongoing focus of the US, "and because this is a part of our broad international effort to try to stem sources of proliferation around the world, so it is an area of ongoing concern." "A Q Khan network is responsible for some of the most serious cases of proliferation in recent decades. We have worked intensively with Pakistan and other countries to shut down that network," he said. "It is something - it's an ongoing focus of ours, and because we - this is a part of our broad international effort to try to stem sources of proliferation around the world. So it is an area of ongoing concern," Crowley said. The Washington Times' article, which talked about the revival of the network, said that scientists, engineers and financiers involved in the A.Q. Khan nuclear-smuggling network are being contacted by several governments in an effort to lure these specialists out of retirement. The development is raising concerns among US intelligence agencies about the revival of the proliferation network that was thought to have been shut down years ago, it said.