The 140 kilogrammes (300 pounds) of radioactive material had arrived without incident in the northern port of Cherbourg early Wednesday aboard a British vessel .

Police threw a heavy escort around as it was offloaded from the ship adespite protests from environmental activists.

A procession of trucks, accompanied by police vans and motorbike outriders, then took the radioactive cargo to the nearby retreatment plant in La Hague, run by the French state company Areva.

A French court on Tuesday issued an injunction banning the activists from approaching within 100 metres (yards) from the cargo on land, and 300 metres at sea.

The transport vessel left North Carolina, on the eastern seaboard of the United States, on September 20, with another British vessel as escort.

After initial treatment at La Hague, the plutonium was to be taken by road 1,200 kilometres (720 miles) across France to the reprocessing plant in the southeastern town of Cadarache.

There, it will be transformed into two tonnes of fuel used in civilian power plants known as mixed oxide, or Mox, and returned to the United States.

Greenpeace activists, who have denounced the long transport route as particularly dangerous for such a deadly cargo, on Tuesday blocked for several hours a road along which the nuclear cargo was due to be taken to La Hague.