A 15-year-old student drew a handgun and opened fire in a school classroom in southern Argentina (search) on Tuesday, killing four classmates and wounding five, authorities said.

Police said the shooting came minutes before the start of classes in the Islas Malvinas public school in Carmen de Patagones (search), a city some 600 miles south of Buenos Aires.

Mario Oporto, education minister for the vast Buenos Aires province where the shooting occurred, said two teenage girls and a boy were killed instantly and a fourth student died soon after at a hospital. At least three of the dead were aged 14-16.

Four of the wounded were treated immediately on the scene and a fifth student was hospitalized in serious condition, authorities said.

Police detained a teenage suspect and were questioning him but said they had no known motive and only sketchy details of what happened. Authorities were planning to transfer the suspect to a juvenile court in Bahia Blanca (search), another city in southern Buenos Aires province.

Police on the scene said students told them the shooter entered the room without saying a word and began firing a 9-millimeter handgun, aiming first at the walls as students cowered beneath desks.

Students who were outside the classroom at the time told local television they thought they heard firecrackers going off, then saw bloodied students screaming as they fled the classroom. They said the shooting began around 7:30 a.m., before the teacher had shown up.

One teenage boy said he was in an adjacent classroom when he heard intermittent shots.

"We heard gunfire and a lot of screaming and then everyone coming out into the hallway," said the boy, who did not identify himself. "We saw three bodies on the ground with bullet wounds."

Outside the school, a crowd gathered along with ambulances, police squad cars and a fire truck. Police removed the bodies while forensic experts remained behind for hours.

The episode touched off a debate on national television about rising violence in public schools in Argentina, home to 36 million people and long considered one of the safest countries in South America.

Stabbings and beatings of students and teachers have been reported in recent weeks, raising public concern about the nation's schools. Surging school violence has also come on the heels of a crime wave in Argentina marked by ransom kidnappings, street shootings and carjackings.

Before traveling to the scene, Oporto told local radio Argentines were grieving over the tragedy.

"This is a case of violence that has exceeded all bounds," Oporto said.