A third bomb exploded on Sunday in Palma de Mallorca, in the Balearic Islands, but no one was injured, police said.
The blast followed two earlier explosions at different restaurants that caused damage to the structures but no injuries.
Police have sealed off the area where the bombs went off.
The latest explosions have confirmed police suspicions that ETA have some type of infrastructure set up on the Balearic Islands.
The blasts occurred after a warning was phoned in to a radio station by an individual who said the Basque terrorist group ETA had planted the bombs, officials said.
The first bomb went off inside the La Rigoletta restaurant and the second exploded at the nearby Enco restaurant, while the third blast occurred in the city's main square.
Dozens of residents and restaurant employees were evacuated from the area.
The bomb at La Rigoletta was apparently inside a backpack that was hidden in the false ceiling of a bathroom.
Police are examining a backpack that "has suspicious characteristics," the chief prosecutor for the Balearic Islands, Bartomeu Barcelo, said.
Bars and restaurants
An individual claiming to be calling on behalf of ETA told Radio-Taxi Guipuzcoa that several bombs planted at bars and restaurants in Palma de Mallorca would explode between noon and 6:00 p.m. on Sunday.
King Juan Carlos has his summer residence in Palma de Mallorca and two Civil Guard officers were killed in the city late last month.
The Basque terrorist group claimed responsibility in a communique on Sunday for four recent attacks that killed three police officers in Spain.
ETA said in a communique published in the online edition of the Gara newspaper, considered a mouthpiece for the terrorist group, that it carried out the attacks in June and July.
National Police inspector Eduardo Puelles was killed by a car bomb in Bilbao, a city in Spain's northern Basque region, on June 19.
Limpet bomb
Civil Guard officers Carlos Saenz de Tejada and Diego Salva were killed on July 30 by a remotely detonated limpet bomb that destroyed their patrol car on Mallorca.
ETA claimed responsibility for the July 29 car-bomb attack on a Civil Guard barracks housing officers and their families in the northern Spanish city of Burgos that wounded more than 60 people and caused extensive damage.
The terrorist group also said it bombed the Socialist Party offices in the Basque city of Durango in early July.
ETA has killed more than 850 people since taking up arms in 1968 to seek a Basque nation comprising parts of northern Spain and southern France.
The terrorist group has carried out about two dozen attacks since June 5, 2007, when it ended its unilateral cease-fire with the Spanish government.
ETA had declared a "permanent cease-fire" in March 2006 in an apparent attempt to negotiate peace with the government of Socialist Prime Minister Jose Luis Rodriguez Zapatero.
Most observers, however, regarded the deadly Dec. 30, 2006, bombing at the Madrid airport as marking the end of the cease-fire.