Spain's election campaign was thrown into disarray yesterday by an apparent act of terrorism, when a politician was gunned down in front of wife and daughter just two days before the vote.

Authorities immediately blamed Eta, the violent Basque separatist group, for the killing of Isaías Carrasco, a 43-year-old former Socialist Party councillor from the Basque town of Mondragón. Mr Carrasco was shot three times in his back and neck outside his home and died in hospital shortly after.

“I was in my room and heard three shots,” a distraught neighbour said on Spanish television. “I looked through my window an saw his wife and daughter on top of him yelling, ‘Murderers, murderers!'. His chest was soaked in blood.”

José Luis Rodríguez Zapatero, the Prime Minister, was ending a campaign rally in Málaga when he heard the news and flew immediately back to Madrid. All political parties suspended their campaigning to hold an emergency session in Congress, condemning Eta's apparent return to political assassinations. If Eta is confirmed as the perpetrator, it would be the first time the group has killed a politician in nearly six years.

The rivals in Sunday's elections joined together to condemn the killing and send their condolences to Mr Carrasco's family.

“The terrorists have today tried to interfere in the peaceful manifestation of the will of the people at the polls,” Mr Zapatero said. “Eta has already been defeated by democracy — rejected and isolated by Spaniards as a whole and by Basque society. Eta has no other destiny than to disappear, and its members have no other future than jail.”

Mariano Rajoy, the candidate for the conservative Popular Party, struck a similar theme. “Today is a day of mourning,” he said. “We will defeat Eta and the killers of Isaías will soon end-up in prison.”

But despite the outward show of unity, behind the scenes, the rival campaigns were scrambling to figure out how the killing could affect Sunday's vote. The conservative Popular Party has made the fight against Eta its main theme during its last four years in opposition, and some believe it stands to benefit from public revulsion over Eta's return to political assassination.

Others believe that the ruling party could receive votes in sympathy with the family of the former Socialist politician.

The former councillor lived in a working-class area of the industrial town of Mondragón with his wife and three children. He retired from politics last year and was working as a toll booth operator on a nearby motorway. He reportedly turned down the armed bodyguard made available to politicians in the Basque Country because of Eta's assassinations.

The Prime Minister had been projected by opinion polls to win on Sunday by a narrow margin. But analysts pointed out that a similar lead by the Popular Party in 2004 evaporated after the Madrid train bombings by Islamic radicals, which killed 191 people.

The conservative government in power then tried to blame the attacks on Eta despite growing evidence that it was the work of Islamic militants, in a move that analysts believe cost it the election.

Eta has killed more than 800 people in its four-decade long campaign for an independent Basque homeland in the north of Spain and the southwestern corner of France. It is deemed a terrorist organisation by the US and European Union.

Mr Zapatero made an ill-fated attempt to negotiate a peace deal with Eta in 2006 after the group called a “permanent” ceasefire and vowed to lay down its arms. However, it broke that ceasefire in December 2006 with a huge bomb blast at Madrid's main airport, levelling a multi-storey car park and killing two people who were not evacuated after telephone warnings. It also killed two Spanish police officers last December in a shootout in southern France.

Eta had recently concentrated its attacks on members of Spain's security services, apparently for fear of alienating its dwindling support base. On Thursday, the fringe Basque political parties that support Eta remained silent on its return to political killings.

Security sources suspect that many supporters will be deeply uncomfortable with the development. Two “historic” members of the group in prison have also broken publicly with the leadership, condemning its decision to restart the campaign of violence.

In recent months, Eta has been weakened by dozens of arrests in France and Spain. Spanish and French security forces have also disrupted several bomb plots. Security analysts believe that Eta has been forced to return to “soft targets” to make itself heard because of its inability to carry out more sophisticated attacks.

But the return to such gruesome methods could further weaken its political support base in the Basque Country. Polls show that between a quarter and a third of Basques support independence from Spain, but only a small fraction of those say they support Eta.

“We have had enough of Eta's violence. We are sick and tired of Eta killing our sons and daughters,” said Juan José Ibarretxe, the president of the Basque regional government. “Never again use the name of the Basque people to justify your murders,” he told Eta.

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