Speaking on Dutch radio programme Argos on Tuesday morning, Lubbers said the Dutch authorities held off from taking action against Khan in 1975 and 1986 because the US security agency wanted to gain more information about the scientist's activities.

Khan was hailed a national hero in Pakistan in 1997 when the then prime minister Nawaz Sharif announced that the country possessed nuclear weapons.

It emerged later that Khan also headed a clandestine network that sold on nuclear know-how to Libya, North Korea and Iran. Although there was mounting evidence of Khan's illicit activities by 2001, this was only made public in 2004.

Born in Bhopal, Khan trained as a metallurgist in Germany. From May 1972 to December 1975 he was employed by Physics Dynamic Research Laboratory (also known as FDO), an engineering firm based in Amsterdam and a subcontractor to the URENCO consortium specialising in the manufacture of nuclear equipment.

Urenco's primary enrichment facility was in Dutch city of Almelo, near the German border. Khan had an office there by late 1974, the website of globalsecurity.org says.

In early 1976, Khan left the Netherlands with secret Urenco blueprints for an uranium centrifuge. He was convicted in absentia by a court in the Netherlands in 1983 for stealing the designs. The conviction was later overturned on a technicality.

Lubbers was the longest serving prime minister in the Netherlands (1982 - 1994). He was appointed UN High Commissioner for Refugees in 2001 but resigned last February due to sexual harassment allegations.

He told the radio station that when Minister of Economic Affairs in 1975 he discussed the Khan case with US officials. The Americans, Lubbers said, suggested blocking Khan's access to Urenco would be sufficient.

As Prime Minister in the mid 1980s Lubbers again raised the issue as the CIA had been monitoring Khan for 10 years, without any obvious breakthrough in the investigation. Again the Americans did not want action taken against Khan, Lubbers said.