The case was part of a kit for geologists to measure the density and humidity of the earth and contained "two sources of low-level radioactivity," said the agency, the CSN.

It disappeared on Tuesday from a vehicule in the town of Mostoles, outside Madrid, and was probably stolen, it said in a statement.

"The material that was removed presents no radiological risk if it remains closed and intact, since the radioactive sources are inside and protected in capsules," it said.

But the material could "pose risks if it is opened or the equipment destroyed," the CSN warned.

The agency released a detailed description of the equipment and an appeal to the public to be careful.

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.