Abdul Qadeer Khan, the man behind Pakistan's nuclear bomb, has been placed under 'certain unspecified restrictions' amid a probe into alleged links between Pakistani nuclear scientists and Iran, Islamabad's Daily Times newspaper reported on Monday.

He had established Khan Research Laboratories at Kahuta near Islamabad and is often referred to as the 'father' of Pakistan's nuclear bomb.

The unspecified restrictions follow the detention and debriefing of two directors of KRL, Yasin Chohan and Farooq Mohammad, who were picked up from their homes in early December, it said. Chohan has since returned home but Mohammad Farooq is still being questioned.

Foreign office spokesman Masood Khan admitted that in-house investigations have been going on for some time. He told the daily that Pakistan had never authorised any transfers of sensitive nuclear technology to other countries.

Islamabad had earlier the three top nuclear scientists after evidence discovered in a probe of Iran's secret nuclear programme pointed to Pakistan as the source of its crucial technology.

Documents provided by Iran to UN nuclear inspectors since early November have exposed the outlines of a vast, secret procurement network that successfully acquired thousands of sensitive parts and tools from many countries, US and European officials told The Washington Post.

Though Iran has not directly identified Pakistan as a supplier, Pakistani individuals and companies are strongly implicated as sources of key blueprints, technical guidance and equipment for a pilot uranium-enrichment plant that was first exposed by Iranian dissidents 18 months ago, government officials and independent weapons experts said.

The blueprints, which the IAEA has reviewed, depict a type of centrifuge that is nearly identical to a machine used by Pakistan in the early years of its nuclear programme, according to US officials and weapons experts familiar with the designs. The plans and components, which were acquired over several instalments from the late 1980s to the mid-1990s allowed Iran to leapfrog over several major technological hurdles to make its own enriched uranium, the report added.