SANTONA, Spain, Sept 22, 2008 (AFP) - Spain's prime minister vowed Monday to bring 'ETA terrorist assassins' to justice after a soldier was killed and 11 people were wounded in a trio of bombings blamed on the Basque separatists.

'Spanish society will never yield. It will never submit to the dictates of the ETA terrorist gang,' Prime Minister Jose Luis Rodriguez Zapatero said at his government headquarters.

'It will hand the assassins to the full weight of the law and justice,' he said, adding that 'they have no other fate than to be arrested, put on trial and sentenced to huge prison terms.'

A soldier was killed and another wounded on Monday when a car bomb exploded outside a military school in the northern autonomous Cantabria region, which is adjacent to the Basque Country.

It was the third attack attributed to Basque separatists in 24 hours.

'Today ETA is killing again,' said Zapatero, who expressed condolences to the wife of the soldier, Luis Conde de la Cruz.

At the annual United Nations General Assembly in New York, UN chief Ban Ki-moon on Monday spoke out against an upsurge in attacks.

'The secretary-general strongly condemns the recent series of car bombings in Spain, which have resulted in one fatality and the wounding of several others,' his spokesman, Michele Montas, said in a statement.

Interior Minister Alfredo Perez Rubalcaba and Defence Minister Carme Chacon travelled to the Cantabrian town of Santona to visit the victim's widow and speak with the other soldier who was injured.

The Basque region's road assistance service received an anonymous telephone warning 35 minutes ahead of the explosion in the early hours of Monday, a spokesman for the service said. The call claimed the attack on behalf of ETA.

The blast caused 'considerable material damage,' according to police in Santona.

De la Cruz is the fifth person killed in attacks suspected to be the work of the militant group since the organisation formally ended a 15-month-old ceasefire in June 2007.

Monday's attack follows two suspected ETA car bombings the previous day.

Ten people were injured after suspected Basque separatists threw petrol bombs at a police station in Ondarroa in the Basque Country to lure officers outside before detonating a car bomb.

That attack came only hours after a car bomb exploded in the Basque regional capital of Vitoria, causing no injuries as another anonymous warning gave police time to clear the area.

Each bomb used around 100 kilogrammes (220 pounds) of explosives.

Rubalcaba said at least two of the three cars used in the attacks, including Monday's bombing, had been stolen in France.

'We are working on the hypothesis that the three cars that exploded were stolen, loaded (with explosives) and prepared in France,' he added.

If confirmed to be the work of ETA, the latest blast would take the number of killings attributed to the group to 824 since it launched its campaign of violence 40 years ago for independence for the Basque region.

These attacks show ETA's 'operational capacity' but not its strength, Rubalcaba said. 'Sometimes, this type of senseless attack is a reflection of weakness,' he said.

The attacks sparked protests Monday in several towns and cities throughout the country, notably in Madrid and in the Basque Country.

Designated a 'terrorist organisation' by the European Union, ETA has carried out a series of bombings, mostly in the northeastern Basque region, since talks with the government collapsed following a December 2006 bombing that killed two people in the car park of Madrid airport.

Its last victim was a policeman who was killed when a car bomb exploded in front of his barracks in the Basque Country on May 14.

Spanish police have detained dozens of suspected members of ETA and its supporters in recent months and Zapatero has repeatedly ruled out any further talks with the group.

Spanish authorities have also moved against parties with links to ETA's outlawed political wing Batasuna.

The country's Supreme Court this month banned two Basque independence parties linked to Batasuna.

The bombings are 'obviously the response' to the Supreme Court's decisions, said Gorka Landaburu, the editor of the Cambio 16 news weekly and an ETA expert.

The Basque regional government's plans to hold a referendum on self-determination for the wealthy northeastern region have also been declared unconstitutional by Spain's Constitutional Court.