A bomb found by police on a rail track near the Spanish city of Zaragoza was the fourth planted by Basque separatists it has emerged.
The bomb was found following information provided by two suspected members of ETA arrested on Wednesday. The pair were arrested in an operation which thwarted an attempt to blow up a train in a major Madrid station on Christmas Eve.
Police seized one man carrying an explosives-packed suitcase as he headed for a Madrid-bound train and later arrested another who had already put a bomb on the same train.
The police source said they suspected that a small explosion on a rail track in northeastern Spain on Tuesday night was also connected to the suspects.
Yesterday, a fourth bomb was found on the Zaragoza to Barcelona railway, where along one stretch traffic was stopped as police combed the area.
Separately, in France on Thursday police said they had found a car containing a stack of letters from ETA demanding Basque businesses pay them "revolutionary tax". Basque businesses have often been the target of suspected ETA violence.