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

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

A boat belonging to the environmentalist group Greenpeace has been on station since Saturday in the Channel off the southern English coast, while on Sunday a dozen sailing boats manned by anti-nuclear activists deployed just beyond the limit of the Cherbourg military zone.

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

Greenpeace has said the long road distances involved in transporting the plutonium caused considerable risk, not least because the cargo's containers could easily be broken open by shoulder-launched rockets.

Cogema, the French state nuclear company, issued a statement rejecting the charges, saying the transport of plutonium was carried out with "all safety guarantees," and that the truck convoy would be unmarked to avoid attracting attention.

The French nuclear processing company Areva took Greenpeace to court to prevent them demonstrating too close to the plutonium convoy.

It was seeking an injunction banning Greenpeace from demonstrating at a distance of less than 100 metres (yards) from the vessels in dock, at less than 300 metres at sea inside French territorial waters, and at less than 100 metres from the overland convoy scheduled to convey the plutonium through France, Greenpeace said.

A court hearing here was set for Tuesday.

A spokesman for the French anti-nuclear group Sortir du Nucleaire originally said activists calculated the ships would arrive late Monday.

But after waiting in vain all night Sunday to Monday, they revised their guesswork, putting back the calculated arrival time to late Tuesday.

Three Greenpeace activists in a flotilla protesting the shipment were released from police custody Monday.

They included French yachtsman Eugene Riguidel, whose sailboat was impounded by the police.

Riguidel's boat was boarded after it touched buoys marking the military zone.

The crew -- Riguidel, Jonathan Castle, first captain of the Greenpeace ship Rainbow Warrior, and Pernilla Svenberg of Greenpeace International in Amsterdam -- were taken into custody for 24 hours.

Protesters have also taken up position along the land route to be followed by the road convoy to the plant at La Hague.

Banners proclaimed "Stop plutonium."

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.