ETA has been responsible for seven earlier car bomb attacks in the city since the end of last year, when it was announced that Barcelona would host the 1992 Olympics.

The Catalan newspaper Avui said it received a warning a few minutes before the blast from a telephone caller claiming to speak on behalf of ETA (Basque Homeland and Freedom). But there was not enough time to evacuate the building before the bomb went off, a store spokesman said.

Barcelona's civil governor, Mr Ferran Cardenal, said police received a telephone warning 45 minutes before the explosion. The caller did not say where the bomb was and police did not find it.

As soon as he heard of the bomb blast, the Spanish Prime Minister, Mr Felipe Gonzalez, abandoned his visit to Brazil to fly back home.

Yesterday's bomb attack occurred in the mid-afternoon rush hour, when the large supermarket attached to a chain of department stores was crowded with people doing their weekend shopping.

Witnesses said the blast caused panic and started a fire at the supermarket. One woman was seen running from the building with her hair in flames.

The bomb is believed to have been placed in a car on the first level of the three storey car park beneath the five-floor store. In another part of the building firemen evacuated 30 people undergoing dialysis in a special kidney unit.

Four of the victims were in critical condition, and 15 were described as serious.

Another two, including the pregnant woman, died, before they could receive hospital treatment. A 30-year-old mother and her two small children were among the victims.

Most of those killed were on the floor below the blast. Because of the thick smoke and fumes, firemen wearing breathing apparatus were only able to reach them after some time. A week ago ETA detonated two other bombs at one of Spain's largest oil refineries in Tarragona, south of Barcelona, causing more than pounds 5 million in damage, and forcing 20,000 people to abandon their homes.

Only an hour before the blast, the Interior Minister, Mr Jose Barrionuevo, confirmed the existence of an ETA commando group in Barcelona. He did not rule out the theory that it had been forced there after the smashing of ETA's Madrid commando last year.