An explosion has damaged the tomb of Spain's former military leader, General Franco, at a huge mausoleum near Madrid.

The newspaper, El Pais, said it received a telephone warning of an attack at the monument from a caller claiming to represent the Marxist guerilla group, GRAPO.

Franco's mausoleum was chiselled out of a granite hillside by Republican prisoners captured during the Spanish Civil War. GRAPO carried out many attacks in the 1970's, during Spain's transition to democracy, and was blamed for killing dozens of people; but correspondents say it has been largely inactive recently.