A van loaded with explosives blew up Friday outside a police station in a Basque city, slightly injuring two officers in what appeared to be the first attack by the separatist group ETA since it called off a cease-fire in June, officials said.

Whoever set off the bomb in Durango, about 25 miles south of Bilbao, fled in a car and then detonated it in a vacant lot in the nearby town of Amorebieta, according to the Spanish Interior Ministry office in the Basque regional capital, Vitoria.

The blast caused serious damage to the Civil Guard station and residential barracks in Durango, shattering windows and damaging police cars parked outside, authorities said. Several nearby apartment buildings were also damaged.

The attack happened shortly after 3:15 a.m. (0115 GMT). There had been no warning, the Interior Ministry said.

"Families and children live in that police station which makes the attack all the more despicable," Paulino Luesma, the Interior Ministry's chief delegate in Vitoria, told Cadena SER radio.

Police believe some 175 pounds of explosives were used in the bomb at the station, the Spanish national news agency Efe said. It was not immediately known how many people were in the station at the time of the attack.

The injured officers were treated for cuts from flying glass, but were released from a hospital in a nearby town several hours later.

The second car blast was not considered an attack, but a means to destroy evidence. No one was hurt, and no damage was reported.

Television images showed residents living in the area came out onto the street in rain, several in their bedclothes, to see what had happened.

"All indications point to ETA," a Vitoria ministry official said on condition of anonymity because of department rules barring publication of her name.

ETA called a cease-fire in March 2006, but grew frustrated with a lack of government concessions in ensuing peace talks, and set off a huge bomb in a parking garage at Madrid's airport on Dec. 30, killing two people. It insisted then that the truce was still in effect, but finally declared it formally over in June, and Spanish security forces have been on alert ever since.

ETA has killed more than 800 people since 1968 in its campaign for an independent Basque state.

Since ETA announced in June it was reactivating "on all fronts," low-level violence by supporters of the group has increased, and Basque business leaders say ETA resumed sending them extortion letters seeking money to fund its campaign.

ETA detonated two small explosive devices July 25 along the route that the Tour of France used when the race dipped into northern Spain for a few hours. No one was hurt.

Interior Minister Alfredo Rubalcaba said recently that security forces had thwarted several attempted attacks by ETA in the past few months.

Following the attack at the airport — just days after Prime Minister Jose Luis Rodriguez Zapatero had declared the peace process to be in good shape — the government halted peace talks with ETA, and the most promising momentum in decades toward an end to the conflict lay in ruins.