"The ships have left and they are on their way to the US," Greenpeace spokeswoman Jean McSorley said.

The two vessels left from Barrow-in-Furness in northwestern England and are scheduled dock in the southern port of Charleston, the group said.

The plutonium is to be "manufactured into experimental nuclear reactor fuel at French facilities operated by Areva" and its subsidiary Cogema, Greenpeace added.

Areva declared that the operation was designed to eliminate surplus stocks of US plutonium left over from the Cold War by recycling it like civil fuel in nuclear power stations.

Greenpeace said the plutonium was to be trucked over 1000 kilometres in France in highly vulnerable trucks to plutonium fuel-manufacturing facilities before being returned to the US next year.

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