Pakistan says initial investigations show that some of its nuclear scientists may have been motivated by "personal ambition and greed" to share sensitive nuclear technology with Iran.
Foreign Ministry spokesman Masood Khan says the Pakistani government is questioning some of its nuclear scientists to determine whether they were involved in transferring such information to Iran.
For the first time he revealed at a news briefing that the founder of Pakistan's nuclear-weapons program, Abdul Qadeer Khan, is also being questioned.
The Information Ministry spokesman says the investigation began five or six weeks ago, triggered by information provided by Iran and the International Atomic Energy Agency.
U.S. newspapers have reported that evidence gathered by American and international officials indicates Pakistan was a source of uranium enrichment technology transferred to Iran and North Korea, as well as some other countries.
Washington said on Monday it accepts Islamabad's assurances that Pakistan is no longer involved in nuclear proliferation.
But the Pakistani government has come under strong criticism from the country's opposition political parties. They argue the international community led by the United States is moving in the direction of forcing Pakistan to roll back its nuclear program.