(Adds quote, background) MADRID, Sept 10 (Reuters) - A large car bomb placed by the Basque guerrilla group ETA near a Defence Ministry office in the northern city of Logrono failed to explode late on Sunday after only the detonator ignited, the government said on Monday. The group telephoned a warning to a Basque newspaper at 11 p.m. (2100 GMT) and 30 minutes later a small explosion was heard in a car park in the city, the capital of the Rioja region adjacent to the Basque country. "It's been a very intense night of vigilance," Logrono's mayor Tomas Santos told state radio. "It was a major charge of explosives placed in the town centre, it could have been a tragedy." Police found about 60 kg (130 lb) of explosives in the car, which had been stolen in France. It was the latest in a series of failed attacks by ETA, which has been hit by a series of arrests, officials said. "The device has now been deactivated," Santos said. Hours earlier, the separatist group vowed to keep up bomb attacks against the Spanish state, saying there was no point in negotiating with the Socialist government. The government broke off an attempt at peace talks last year and ETA declared an end to a ceasefire in June. The end of talks meant failure for one of Prime Minister Jose Luis Rodriguez Zapatero's key policy gambles. But it also deprived the conservative opposition, which had criticised them throughout, of a key angle of attack ahead of parliamentary elections due in March. In the Basque city of San Sebastian, police broke up a rally on Sunday in support of ETA prisoners and arrested the leader of an amnesty movement and eight other people while several people were hurt in clashes. Polls show most Basques do not want independence from Spain, the cause for which ETA has killed more than 800 people. The group's four decades of armed struggle began in the last phases of the Franco dictatorship, when Basque culture and language were repressed.
