AFP - A car bomb on Mallorca killed two police officers Thursday in an attack which Spain's Prime Minister Jose Luis Rodriquez Zapatero, expressing "rage and pain," blamed on ETA.

Spanish authorities closed all ports and airports on the island, a popular holiday destination, for several hours after the booby-trap bomb detonated under the officers' vehicle outside a barracks in the coastal town of Palmanova.

"Carlos Saenz de Tejada Garcia et Diego Salva Lesaun were killed today by ETA. I want to condemn this new low blow with much rage and pain but also with much determination," he said in a televised address.

"The criminal attack comes at a time when the civil guards and national police, with the cooperation of French security forces, are striking against the terrorist group as never before," he added.

The prime minsiter said ETA members "are being arrested earlier and in greater numbers and this is the way it will continue to be."

The powerful blast, which went off at around 2:00 pm (1200 GMT), turned the guards' official vehicle into a fireball, television footage taken shortly after the blast showed.

The two civil guards, aged 27 and 28, died almost instantly, the Balearic Islands' regional government said.

Several other people were injured in the explosion.

Hours later, police defused a second booby-trap bomb found under another civil guard vehicle.

"A second bomb placed under an official vehicle was found at another barracks than the one affected by the first attack. It was then defused," a civil guard spokesman said.

While there was no immediate claim of responsiblity, Spanish media said the bombing bore similarities to previous attacks by the Basque separatist movement which marks its 50th anniversary on Friday.

The attack in Mallorca came a day after 64 people were wounded in a car bomb outside a police barracks in northern Spain which authorities blamed on ETA.

The area where Thursday's blast occurred is near the island's capital Palma, a magnet for tourists and only a few kilometres from the Marivent palace where Spain's royal family traditionally spends its summer holiday.

ETA attempted to kill King Juan Carlos in 1995 while he was on the island, and later, the leader of the conservative opposition party and future Prime Minister Jose Maria Aznar.

"We saw a big explosion, a column of smoke in front of the civil guard barracks and a four-by-four vehicle fly through the air," a man named Paco who witnessed the attack told public radio RNE.

The temporary closure of the Mallorca's ports and airports came at the height of the tourist season which is the lifeblood of the island's economy.

A total of 22.8 million passengers passed through Palma airport last year, making it the third busiest in the country, according to AENA figures.

The European Commission condemned what it called a "barbaric" attack.

"The Spanish institutions and citizens should understand that they have the complete solidarity of the European Commission in the fight against terrorism," it added in a statement.

Wednesday's attack in the northern city of Burgos also caused outrage in Spain, with the government accusing ETA of wanting to kill dozens of women and children who were sleeping inside the police barracks.

ETA will on Friday mark the 50th anniversary of its founding by nationalist students inspired by Marxist-Leninist teachings, at a time when Spain was still run by right-wing dictator Francisco Franco.

It is blamed for the deaths of over 820 people as part of its campaign for an independent Basque homeland encompassing parts of northern Spain and southwest France.

Spanish newspaper El Mundo said on Sunday that security forces were on the alert after receiving information from France that ETA planned to bring three vans packed with explosives into Spain.

Spanish public television last month said a new "road map" of strategic plans by ETA reaffirmed its commitment to violence to achieve its aims.

"The terrorists believe that Basque independence is their irreversible goal. Only then will ETA no longer kill," TVE said, quoting a document that it said outlined the group's strategy put together over the past three years.

The last fatal attack blamed on ETA was on June 19, when a policeman was killed in a car-bomb blast near the Basque city of Bilbao.