Palma de Majorca  - Police on Friday stepped up security measures following a bomb blast that killed two police officers on the popular Spanish tourist island of Majorca.

Authorities suspect militants of the armed Basque separatist group ETA are responsible for Thursday's attack, the second attributed to ETA in two days as it marks its 50th anniversary on Friday.

Prime Minister Jose Luis Zapatero urged police to intensify its fight against ETA and improve protection measures for its officers.

In its manhunt, police searched vehicles on Majorca and were looking for an apartment where the attackers may have stayed.

Palma airport was reopened Thursday after a closure lasting one hour and 40 minutes, which led to delays but no cancellations of flights, the airport authority AENA said. The closure had a knock-on effect in many European airports, that reported delays owing to rescheduling.

The attack occurred near police offices in the tourist resort of Palmanova on the western coast. A police four-wheel-drive vehicle blew up after two officers got inside.

Police later discovered another bomb attached to a police car close to a nearby police barracks. Local residents were evacuated before the bomb was detonated in a controlled explosion.

A mourning service for the two killed officers is scheduled for Friday. Crown Prince Felipe, Prime Minister Zapatero and conservative opposition leader Mariano Rajoy are expected to attend.

"ETA must know that we democrats are much stronger and will defeat the terror," Interior Minister Alfredo Perez Rubalcaba said.

ETA, which is listed as a terrorist organization by the European Union and the United States, has killed some 850 people in its campaign for a sovereign Basque state. Its attacks have claimed three lives this year, all of them police officers. (dpa0