The shipment may have been headed for North Korea's nuclear weapons program

The three are alleged to have plotted to export more than 200 aluminium tubes to North Korea, via China.

Prosecutors suspect the alleged despatch could have been used in North Korea's nuclear weapons program.

German authorities believe the British-made tubes were in fact ordered by a North Korean state company.

The main suspect is a 57-year-old manager of a German company who was arrested on 9 April, a spokesman for the Stuttgart prosecutors said.

He was charged with breaching German weapons export laws by failing to obtain a government permit for the shipment.

Shipment intercepted

Two Hamburg-based associates were charged as accessories, spokesman Eckhard Maak said.

The 57-year-old businessman is alleged to have links to a shipment of some 22 tons of aluminium tubes, officially headed for China, which was intercepted aboard a French-flagged ship in the Mediterranean.

The businessman is said to have claimed that the tubes were for use in gas tanks in Chinese aircraft.

The suspects' identities have not been released and investigations into the case are continuing.

North Korea has been involved in a nuclear stand-off with the United States since October 2002, when the US accused Pyongyang of trying to enrich uranium in defiance of a 1994 accord.

That sparked a crisis which saw North Korea eject UN nuclear inspectors and claim to have restarted operations at its Yongbyon nuclear plant.

North and South Korea, the US, Japan, China, and Russia are set to meet in Beijing on 27-29 August to discuss the crisis.