MADRID, Spain (CNN) -- For the second time in three days, a bomb went off in northern Spain Sunday preceded by a warning call by the Basque separatist group ETA.
Police cordoned off the area around the blast and evacuated residents.
The blast damaged the recreation center of the ruling Socialist Party in the Basque town of Elgoibar. No one was hurt, reported CNN's partner station, the 24-hour Spanish language news channel CNN Plus.
About an hour before the 3:25 a.m. blast, someone claiming to represent ETA called authorities warning them of the bomb, CNN Plus said.
Police cordoned off the area, evacuated some residents and ordered others to remain inside.
On Thursday, seven Basque police officers were slightly hurt when a bomb exploded on the outskirts of Bilbao -- also in northern Spain.
In that case as well, an early morning call to police in the name of ETA warned of the imminent explosion. Watch police inspect the damage ».
ETA threatened the Socialist Party after the re-election last month of Prime Minister Jose Luis Rodriguez Zapatero and reiterated its long-standing call for independence for the Basque region.
ETA has warned that it would not remain "with crossed arms" while its political arm remains illegal.
On March 7, two days before Zapatero won re-election, ETA was blamed for the fatal shooting of a former town councilman from the Socialist Party in a northern Basque town.
The group declared a unilateral cease-fire in March 2006, raising hopes for an end to the violence. However, an ETA bomb at Madrid's airport in December 2006 killed two men, destroyed a parking garage -- and ended the peace process.
ETA officially terminated the cease-fire in June 2007, and since then the government has blamed it for three killings: two undercover Spanish Civil Guards who were shot dead in France while on an anti-terrorist operation against ETA, and the former councilman killed on March 7.
ETA is blamed for more than 800 deaths in its long fight for Basque independence. E-mail to a friend