Powell, who will fly to Islamabad Wednesday after a visit to neighbouring India, said Pakistani President Pervez Musharraf was "as determined as we are" to put an end to proliferation of nuclear technology.
"But we can't be satisfied until the entire network is gone, branch and root," Powell told a joint press conference with Indian Foreign Minister Yashwant Sinha.
Khan, the father of Pakistan's nuclear bomb, last month publicly confessed that he had shared nuclear secrets with Iran, Libya and North Korea.
Musharraf pardoned Khan, who is revered as a national hero. Pakistani officials have described the scandal as the work of rogues working without government support.
Powell said that if any past or present Pakistani government official was involved in the nuclear proliferation, "I will speak to Musharraf about this."
"We are pleased that we are getting a great deal of information from Pakistani authorities as a result of their interrogation of Dr Khan and his associates. We are pleased that this network is being broken up," Powell said.
He added: "We learned more about it when the Libyans decided they should get rid of their weapons of mass destruction."
Libya said December 19 that it was abandoning all attempts to develop weapons of mass destruction, after months of secret negotiations with Britain and the United States.
Powell said no decision had been made on Pakistan's renewed requests to obtain F-16 fighter jets.
He said an aid package for Pakistan unveiled by US President George W. Bush last year "did not include F-16s."
"We have to take into consideration any requests that are made of us, but no decision has been made with regard to any particular military package, especially F-16s," Powell said.
Pakistan, India's historic rival, is a frontline ally in the US-led war on terrorism.