Spain's Socialist Party led by Prime Minister Prime Minister Jose Luis Rodriguez Zapatero is claiming victory in Sunday's parliamentary election. With about half of the vote counted, official returns put the Socialists at least 10 points ahead of the opposition conservative Popular Party, led by Mariano Rajoy. But it appears the Socialists will be re-elected without an absolute majority in the lower house of parliament and will have to rely on the backing of other parties to get legislation passed. Sabina Castelfranco reports from Rome.

Some 35 million citizens are eligible to vote in Sunday's general election, 1.2 million of them live abroad. They will cast their ballots to elect a new congress, made up of 350 deputies, and a new senate, made up of 208 members, for the next four years.

Voters will have to decide whether to give Socialist Prime Minister Jose Luis Rodriguez Zapatero a second term. He is favored slightly over the conservative Popular Party led by Mariano Rajoy, who lost in 2004.

The campaign has focused on concerns over a weakening economy. Economists say growth could fall from 3.8 percent last year to as low as two percent this year, a rate not seen since the early 1990s.

Unemployment in Spain is also a problem. It is rising faster than anywhere else in Europe, reaching more than 8.5 percent in January. It is expected to rise above nine percent this year.

Many in Spain are also unsettled by an unprecedented influx of more than three million registered immigrants in the last eight years. The Popular Party leader Rajoy has linked immigrants to rising crime and blamed them for strains on the welfare state.

The election has also been overshadowed by the killing on Friday of a former Socialist councilor by suspected Basque separatists. Thousands of people mourned the death of Isais Carrasco on Saturday, turning what was supposed to be a quiet day of reflection before the vote into a day of grief.

The shooting prompted Spain's political parties to call off their final rallies on Friday as campaigning was drawing to a close.

Victor Sampedro, a university professor and expert in political communication, described the killing as the work of 'desperate' people because it showed the impotence of ETA. He said Carrasco did not have an elected political role anymore. He said he was just a Socialist Party militant. The killing, he added, showed the political emptiness of ETA.

For many Spaniards, the timing of the violence was reminiscent of the March 2004 train bombings that killed 191 people in Madrid three days before elections. But it is unclear whether Sunday's election will be affected by the councilor's killing.

Observers have said there could be a wave of sympathy benefiting Socialist Prime Minister Jose Luis Rodriguez Zapatero or a backlash against him for negotiating in vain with the armed separatist group ETA.

Efforts by the Socialists to negotiate with ETA failed when it broke a truce by detonating a car bomb that killed two people at Madrid airport in December 2006.