Police and firemen took two hours to cut loose the dozen protesters who had attached themselves under and inside the vehicle, which had the words "Stop Plutonium" written on its side next to a nuclear symbol.

The truck itself was immobilised by a big metal slab, blocking the road leading to the Cogema nuclear recycling facility in La Hague, near the town of Cherbourg.

Greenpeace members said all of those who took part in the protest were arrested.

A spokeswoman for the state-owned plant, Laurence Pernod, criticised the action as "a media-seeking gesture designed to fool the public".

She added: "We don't understand how a militant organisation that has always been against nuclear weapon proliferation could rise up against an operation meant to neutralise them."

Two British-registered vessels carrying 140 kilograms (308 pounds) of plutonium from US weapons arsenals were expected to dock in Cherboug after a voyage from North Carolina.

The plutonium is to be taken to the French nuclear reconditioning plant at La Hague, then sent to a facility in southern France to be recycled and eventually returned for civilian use in the United States.

One Greenpeace militant at the protest, a German named Thomas Breuer, said the organisation wanted "to focus attention on this very dangerous and completely unneccesary transport."

Greenpeace has said the long distances of road transport involved constituted "considerable" risk, not least because the cargo's containers could easily be opened by shoulder-launched rockets.

Authorities have kept the docking date and hour a strict secret, citing security reasons, and forcing protesters to hold all-night vigils at the port.

At a court hearing later Tuesday the French nuclear processing company Areva was hoping to gain an injunction banning Greenpeace activists from approaching the vessels or overland convoy.

The court action came after police on the weekend broke up a Greenpeace flotilla and arrested three activists, who were released Monday.

In a matter not directly related to the US shipment, a truck carrying 4.5 tonnes of enriched uranium was hit from behind by another heavy vehicle transporting mobile telephones early Tuesday near the central city of Orleans, south of Paris.

"The load of radioactive material was not damaged," regional authorities said in a statement.

It added that no-one was hurt in the accident and the motorway the vehicles were travelling on was not closed to traffic.

The truck -- which had no escort -- had been carrying the uranium from Germany to a nuclear power plant in southern France where it was to serve as fuel.

One official, Julien Charles, said the cargo would be transferred to another truck which would complete the journey, this time with an escort.

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