British Nuclear Fuels (BNFL) has accused Greenpeace of "gross irresponsibility" in broadcasting the position of the Pacific Pintail, being escorted by the Pacific Teal.
The Pacific Pintail, in the Southern Ocean and heading for the United Kingdom, is transporting a shipment of MOX nuclear fuel from Japan.
BNFL spokesperson Paul Vallance said Greenpeace had used a publicly available radio channel to broadcast the position of the vessels.
"Greenpeace has to decide what its motivations are. Either this shipment is dangerous and potentially a target for terrorists as they claim - or they must admit that their sole motivation is to stage dangerous stunts for the benefit of the media," Vallance said.
The Greenpeace vessel Esperanza, in Cape Town for the duration of the World Summit on Sustainable Development, left the harbour on Saturday and staged a protest on Monday after tracking down the two ships in the Southern Ocean. - Sapa