MADRID, April 4: Three suspects in the Madrid railway bombings blew themselves up as police prepared to storm their apartment, setting off a powerful explosion that killed one special forces agent and wounded 15 police officers, the interior minister said.

Saturday's news further shocked Spaniards, still traumatized by the March 11 bombings that killed 191 people and wounded more than 1,800. An unexploded bomb found on Friday by a high-speed rail track added to the country's uneasiness.

The blast in Leganes, a southwestern suburb of Madrid, blew out part of the exterior walls on the first two floors of the brick apartment building. After the blast, floodlights lit up the wreckage in the exposed rooms of the building. Pieces of concrete littered the floor and wires dangled from the ceilings.

Television footage showed smoke billowing into the dark sky behind buildings in a built-up area, and a handful of people fleeing down the street. In addition to the three suspected terrorists, one special forces agent was killed and 15 police officers were wounded, Interior Minister Angel Acebes said. The injured officers were taken to hospitals, including Severo Ochoa Hospital in Leganes, where three of them were listed in serious condition.

The interior ministry said the police began approaching the building around 7pm (1700 GMT) to make the arrests when the suspects spotted them from a window and began shooting, chanting loudly in Arabic. No police officers were hurt by the gunfire.

"The special police agents prepared to storm the building and when they started to execute the plan, the terrorists set off a powerful explosion blowing themselves up," Acebes said. Police had evacuated residents from the area, and low-flying helicopters used searchlights to scan the buildings.

The minister said a preliminary investigation indicated that three suspected terrorists had died, but he added the number had yet to be confirmed because of the damage to the bodies. He added that police believe those killed may have helped carry out the March 11 train bombings.

The news agency Europa Press reported that forensic police and fire fighters were searching the building's swimming pool for a possible fourth body. This could not be confirmed independently. "There are three that could have blown themselves up, but the possibility of more is not ruled out," Mr Acebes said at his news conference.

"Police believe some of the terrorists that could have died in the explosion, could have been some sought by the security forces as the alleged perpetrators of the killings of March 11," the minister said. -APP