The move followed requests from magistrates in Germany and Switzerland who are investigating alleged trafficking of equipment to enrich uranium in Libya between 2001 and 2003, the public prosecutor's office in Vaduz said.

The Swiss end of the probe is focusing on three unidentified Swiss residents who are suspected of helping to develop gas centrifuges.

The precision equipment is essential to enrich uranium that can be used to produce either nuclear reactor fuel or a nuclear bomb.

The Swiss federal prosecutor's office has accused the three, a father and his two sons, of breaking laws on arms exports and money laundering.

An engineer, Gotthard Lerch, went on trial in the German city of Mannheim in March, on charges of supplying Libya with nuclear weapons technology through a smuggling network organised by disgraced Pakistani scientist Abdul Qadeer Khan.

Lerch, who has denied the charges, was extradited from Switzerland last year.

Libya announced in 2003 that it was giving up efforts to build nuclear, chemical and biological weapons. The move helped end the North African state's international isolation.

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