Thousands marched in Spain to condemn ETA as tearful families mourned two young policemen killed in a bombing blamed on the Basque separatist group which marked its 50th anniversary on Friday.

The prime minister and royal family at a memorial service honoured the officers slain in Thursday's attack on the island of Majorca, and the government put security forces on maximum alert for more possible attacks.

In the evening, thousands rallied in Palmanova, the Majorcan resort struck on Thursday, and in Burgos, northern Spain, where a massive car bomb outside a police barracks on Wednesday injured 64 people including several children.

"All together against terrorism" read one banner at the Majorca rally, which was attended by local officials and families of the two victims.

The violence had flared in the run-up to the anniversary of the movement, which has fought for 50 years for an independent Basque homeland in a campaign of violence that has now killed a total of 828 people.

Police also found a second bomb in Majorca on Thursday under another police car at a separate barracks and carried out a controlled explosion.

Prime Minister Jose Luis Rodriguez Zapatero blamed the attacks "on the terrorist group ETA" and vowed to bring all members of the outfit to justice.

"I want to assure citizens that the government has instructed security forces to be on maximum alert, that they redouble their dedication, that they boost even more their efforts and also that they protect themselves from these vile assassins," he said on Thursday.

The attackers "have no chance to hide, they can't flee, they can't escape justice, they will be detained, they will be sentenced, they will spend their lives in jail," he added.

The interior ministry released Friday the photos of six suspected members of ETA — two women and four men — without specifying whether they are believed to have played a role in the bombings in Burgos and Majorca.

Posters containing photos of the wanted suspects will be put up at train stations, airports and other public areas, the ministry said.

The authorities closed all Majorca's ports and its airport — the third busiest in Spain — for several hours after the bomb detonated, disrupting travel plans for thousands of tourists during the peak holiday season.

Ports on the island were operating normally on Friday but boat traffic was facing tighter controls than usual, a spokesman for the port authority on the Balearic Islands said.

"Boats cannot enter or leave the island without the authorisation of the civil guard. There are only slight delays affecting passengers due to search operations," he said.

Police were working on the hypothesis that those responsible for the bombing had not left the island and were hiding in an apartment "waiting for the situation to cool down", the central government's representative on the islands, Ramon Socias, told reporters.

Crown Prince Felipe and his wife Letizia embraced members of the slain officers' families as they arrived at Palma de Majorca's main cathedral for the memorial service for the two: Carlos Saenz de Tejada Garcia, 28, and Diego Salva Lesaun, 27.

Earlier on Friday the prime minister posthumously awarded the two men with the Gold Cross of Merit, the highest award available to members of Spain's armed forces, as their family members, some of them in tears, looked on.

Speaking in the Portuguese island of Madeira where he was on an official visit, Spain's King Juan Carlos condemned the "savage attacks" in Majorca and Burgos.

"Terrorism this week once again showed its most cowardly and despicable face," he said.

ETA was formed on July 31, 1959 by a group of left-wing nationalist students opposed to General Francisco Franco's right-wing dictatorship, which suppressed the Basque language.

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.

AFP