At least one small explosion hit the Spanish section of Wednesday's Tour de France cycle race after a report of a bomb threat from a caller claiming to represent Basque separatist rebels ETA, the government said.
No one was hurt and the Tour, the most important race on the cycling calendar, continued after the explosion.
The caller told a highway authority that ETA had planted several bombs along the route of the Tour de France through the Spanish region of Navarre, newspaper El Pais and other media said.
"At least one device, of little power, has exploded in Belagua, Navarre," an Interior Ministry spokesman said. El Pais said two bombs had gone off.
The race had already passed through the small town of Belagua at the time of the incident, local media reported.
ETA has killed more than 800 people in four decades of armed struggle for traditional Basque lands in northern Spain and southern France. It called off a ceasefire in June.
The government says it has foiled several plans for bomb attacks by ETA since December when a bomb it planted at Madrid airport killed two people, even though the ceasefire was still meant to be in force.
An ETA member was arrested in the south of France on Wednesday, the Spanish government said.
The rebels have threatened the Tour de France before.
The Tour, in its final week, has been engulfed in controversy after pre-race favorite Alexander Vinokourov tested positive for blood doping.
Dane Michael Rasmussen held an advantage of two minutes 23 seconds over Spain's Alberto Contador ahead of Wednesday's 218.5-km 16th stage to the Col d'Aubisque, one of the most spectacular in this year's race.
Rasmussen is also under pressure after failing to provide information on his whereabouts during training.