Police have found a bomb on a Spanish rail track which a police source says is the fourth set up by two suspected Basque separatists arrested on Wednesday for trying to blow up a train.
Police arrested the two suspected members of Basque separatist group ETA, thwarting an attempt to blow up a train in a major Madrid station on Christmas Eve, one of the busiest travel days of the year.
They 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 on Friday a small explosion on a rail track in northeastern Spain on Tuesday night was also the pair's work.
"We are presuming that the four bombs were set up by those two people," he said.
The fourth bomb was found on the Zaragoza to Barcelona railway, where along one stretch traffic was stopped on Thursday as police combed the area.
The bomb was being deactivated on Friday.
ETA, which has killed some 850 people in its campaign for an independent Basque state since 1968, has attempted to stage Christmas bomb attacks before.
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.