MADRID (Reuters) - An explosion on Wednesday damaged the tomb of former dictator Francisco Franco in Spain`s Valley of the Fallen, a huge mausoleum carved out of a hillside near Madrid, a fire brigade official said. No one was hurt in the blast, which caused some damage to the area around the altar in the cavern that was chiselled out of the granite by Republican civil war prisoners. A journalist at El Pais newspaper said someone claiming to represent the Marxist guerrilla group GRAPO called the paper more than one hour before the explosion to say it intended to attack the monument. The journalist told Reuters the newpaper informed the police before the blast. GRAPO, which stands for October First Anti-Fascist Resistance Group, was active mainly in the early years of Spain`s transition to democracy in the 1970s. It was blamed for dozens of killings then but has been largely inactive recently. The Valle de los Caidos, the Valley of the Fallen, is one of the few relics of the bloody conflict that tore Spain apart between 1936 and 1939 and ushered in more than three decades of iron fisted rule under Franco. Crowned by a giant stone cross, the monument attracts a small group of Franco`s supporters each year on the anniversary of his death in November 1975.