Two small explosions scattered rocks and dirt Tuesday along a portion of the Tour de France route that dips into northern Spain, said Spanish officials.
No one was hurt in the blasts, which happened about 40 minutes apart on bluffs overlooking either side of the road.
Officials said they received a telephone call from the Basque separatist group ETA before the explosions.
A caravan of Tour-related publicity vehicles had passed by the site before the blasts, which happened in the town of Belagua in the Navarra region.
The riders passed through without incident about 30 minutes after the second blast.
Reports said Spanish officials found plastic food containers containing a small amount of explosives and that the blasts kicked up some dirt, but caused no injuries.
ETA has claimed responsibility for more than 800 deaths since the late 1960s in its campaign for an independent Basque homeland in northern Spain and southwest France.
The Tour de France route crosses sections of the German and Spanish borders as riders spend close to a month racing over more than 3,500 kilometres.
It finishes in Paris on Sunday.With files from the Associated Press