By Zaffar Abbas BBC correspondent in Islamabad

The government suspects nuclear secrets may have been leaked

Several of the country's most senior scientists, including Abdul Qadeer Khan, have been questioned.

The government says many of those detained have now been released but nine are still being "de-briefed".

The entire investigation into the possible transfer is being carried out in utmost secrecy.

It started more than a month ago after the International Atomic Energy Agency shared with Pakistan the information it had gathered from Iran and Libya about their nuclear programmes.

Information Minister Sheikh Rasheed Ahmed said Pakistani investigators were sent to Iran and Libya and on the basis of their reports the authorities had started the de-briefing sessions with a group of scientists and officials.

But Mr Ahmed refused to say if any evidence was found about the involvement of these individuals in transferring nuclear know-how to either Teheran or Tripoli.

'Scapegoats'

He said some of the scientists had already been de-briefed but nine officials and scientists were still being questioned.

Among those being interrogated was Mohammed Farooq, who was once closely associated with the country's top nuclear scientist, Abdul Qadeer Khan.

Mr Farooq was the first to be picked up by the authorities and it appears the investigation has so far centred round his past activities.

But the information minister refused to be drawn on this point and said more details would be given once the probe concludes in a week's time.

He described media reports about the government's possible role in the proliferation as baseless but if any individuals were found to be involved they would be dealt according to law.