Police found a second bomb under another police jeep later Thursday in the same area and carried out a controlled explosion. Authorities temporarily blocked all outgoing flights and ships from leaving Mallorca as part of a manhunt.
Less than 36 hours earlier, a car bomb destroyed a police barracks in the northern Spanish city of Burgos, injuring about 60 people Wednesday.
If confirmed as ETA attacks, the blasts would conflict with government assertions that the group is seriously weakened after major police crackdowns in Spain and France in recent years.
The 50th anniversary of ETA's founding is Friday and the group may be trying to demonstrate with attacks on the two consecutive days before the milestone that it was not in any danger of breaking up.
The officers killed Thursday were aged 27 and 28. They belonged to the paramilitary Civil Guard, which is chiefly in charge of policing rural areas and guarding official buildings.
Television images showed the charred and mangled remains of a vehicle that had been parked on a street in the Palmanova beach resort area, southwest of the island's capital, Palma de Mallorca.
The blast was caused by a bomb attached to the underneath of the vehicle, Interior Ministry official Ramon Socias said. Police believe the attack was carried out by an ETA cell that came to the island specifically to carry it out and was not based there, he said.
The island's airport and ports were closed shortly after 4 p.m. (1400 GMT, 10 a.m. EDT) and reopened just under two hours later, police said.
Mallorca, with its golden sandy beaches, mild Mediterranean climate and crystal clear waters is one of Europe's main tourist destinations and the explosion occurred at the height of the summer holiday season.
In June, about 2.6 million passengers used Mallorca airport while more than 22 million passed through it last year.
Most of the tourists come from Britain and Germany and tour operators said they were trying to make contact with them. A spokeswoman for British travel organization ABTA said there were an estimated 15,000 to 20,000 Britons on the island Thursday.
The blast occurred shortly before 2 p.m. (1200 GMT, 8 a.m. EDT). The ministry said several people were injured but none was in serious condition.
Prime Minister Jose Luis Rodriguez Zapatero will fly to the island later Thursday.
ETA is now blamed for nine attacks this year. The group has killed more than 825 people since it launched its violent campaign in 1968 for an independent homeland in the Basque region of northern Spain. The group was founded July 31, 1959.
There were no warning calls before the attacks over the past two days and no group had claimed responsibility.
In Wednesday's attack, there were around 120 people in the 14-story barracks and surrounding buildings, a third of them children, at the time of the early morning blast.
The van had false license plates and had probably been stolen in France, officials said.
El Mundo newspaper recently reported that Spanish authorities had received intelligence reports that three vans had been prepared as car bombs and were expected to cross into Spain from France. One of the vehicles mentioned was a Mercedes Vito, the same model that was used in Wednesday's attack, leading to speculation there might be two van bombs still ready to be used.
Spain has vowed to crush the separatist group since ETA ended what it had said was a permanent cease-fire with a bombing that destroyed a Madrid airport parking garage and killed two people in 2006.