The official told AFP late on Sunday:"Dr Qadeer and four others have accepted that they were involved in leaking nuclear know how outside Pakistan to groups working for Iran, Libya and North Korea," the official who could not be named said.
Nuclear pioneer Dr Abdul Qadir Khan is the father of Pakistan's nuclear programme and is regarded as a national hero in the country.
The information was leaked between 1986 and 1993, he added.
The official said an 11-page report carrying the confessions has been submitted to President General Pervez Musharraf.
Asked if there would be criminal proceedings against those who have confessed he said: "It is up to the National Command Authority to take a decision of which the President Pervez Musharraf is the chairman."
It was not yet clear whether Khan had admitted to giving centrifuge designs for uranium enrichment to Iran and Libya, he said.
Another government official has said Musharraf may address the nation soon after the Muslim festival of Eid al-Adha which begins in Pakistan on Monday.
In Switzerland last week, President Musharraf said it was likely Pakistani scientists had leaked nuclear secrets, and promised a crackdown.