THREE suspects wanted for the Madrid train bombings set off a bomb when cornered in a flat, killing themselves and a policeman, as Spain?s search for the perpetrators of the attacks went wrong.

Spanish news agency Europa Press, quoting security force sources, said the suspects were among six men for whom Spain issued arrest warrants on March 31 in connection with the March 11 attacks on Madrid commuter trains that killed 191 people.

Police swooped on the working-class Madrid suburb of Leganes on Saturday evening in an attempt to round up several suspects. The operation turned ugly when the occupants of the first-floor flat, said by neighbors to be Moroccans in their 20s, spotted the police and began firing while shouting and chanting in Arabic, officials and local residents said.

The police were about to raid the flat when the suspects set off an explosion, demolishing the front of the five-storey apartment block. ?There are three bodies of suspected terrorists who may have killed themselves?, Interior Minister Angel Acebes told a late-night news conference.

A police officer of the elite Special Operations Group was also killed and 11 police were injured, Acebes said. The powerful blast sent a pall of smoke into the air, left a gaping hole in the front of the block, damaged nearby buildings and left a pile of rubble on the ground.

Police cordoned off the area. Residents of surrounding blocks were evacuated and 30 families had to spend the night at a hotel because they could not return to their damaged homes.

Europa Press said the blast blew the three bodies up to 30 metres (90 feet) from the living room of the apartment, and police were checking the building?s swimming pool for a possible fourth suspect?s body.

?This is a very quiet neighborhood. There?s no conflict here. But it?s places like this where these people try to hide?, said local resident Juan Manuel Velez. Spain is holding 15 people, many of them Moroccan, over the March 11 attacks. Acebes has singled out the Moroccan Islamic Combatant Group ? a shadowy organization believed to be tied to Osama bin Laden?s al Qaeda network ? as prime suspect in the bombings.

He said one suspect in the flat may have escaped before the police cordoned off the area but he could not be sure. Acebes said earlier on Saturday a bomb found on a high-speed rail track on Friday contained the same make of explosive and may have a similar detonator to the March 11 bombs. However, officials cautioned that both the explosives and detonators are widely used in mining.

Unused detonators found

Europa Press said police also found unused detonators in the ruins of the Leganes apartment. Investigators believe extremists planned to derail a high-speed train in an attack that might have killed hundreds. The government refused to blame any group for Friday?s thwarted bomb.

High-speed trains from Madrid to the southern city of Seville began running again on Saturday after the 12-kg bomb was defused. Police and army backed by helicopters and armoured vehicles, were guarding the line but passengers were nervous.

?It always affects you. You can?t be calm. Everything seems fairly under control...but there could have been another March 11 yesterday?, said 40-year-old chemist Jose Antonio Perez.

Trains that would normally have been packed with travellers leaving town for the Holy Week holiday had lots of empty seats. El Pais newspaper said Spain, a strong supporter of US policy on Iraq under outgoing Prime Minister Jose Maria Aznar, was the main al Qaeda base in Europe and that police believed it could strike here again.

Furthermore, Spanish Interior minister Angel Acebes said yesterday that two suspected members of armed Basque separatist group ETA have been arrested in France and a large cache of arms and explosives have been found. The discovery of the arms cache follows the arrest of three ETA leaders in France in the last few days.

Nevertheless, socialist leader Jose Luis Rodriguez Zapatero, who takes office later this month after his surprise victory in elections three days after the Madrid bombs, has pledged to bring 1 300 Spanish troops home from Iraq if the United Nations does not take charge there by the end of June.

Daniel Flynn