Three teenagers died at the scene

The shooting happened before the start of class at a school in Carmen de Patagones, 620 miles (1,000km) south of Buenos Aires.

Witnesses said the boy entered the classroom and began to shoot using a 9mm pistol.

Police arrested the boy and took him for questioning.

Two girls and a boy, aged between 15 and 16, died at the scene. Authorities originally said another girl had died but later issued a correction.

Correspondents say the incident sparked debate on national television about rising violence in schools in Argentina, which is considered one of the safest countries in South America.

No warning

The teenager entered the room at the Islas Malvinas state school without saying a word, witnesses told police.

The boy pulled the weapon out from under his clothes and began to shoot Eduardo Diego Local police chief

"There was no kind of aggression nor verbal warning," local police chief Eduardo Diego said on television.

"The boy pulled the weapon out from under his clothes and began to shoot."

Witnesses said the boy, nicknamed "Junior", aimed first at the walls, as students hid beneath desks.

'Timid boy'

Students outside the classroom said they thought they heard firecrackers going off.

"We heard gunfire and a lot of screaming and then everyone coming out into the hallway," a teenage boy was quoted as saying by the Associated Press news agency.

"We saw three bodies on the ground with bullet wounds."

The youth is said to be the son of a coast guard officer. He is believed to have used his father's handgun.

The suspect had no history of violence, officials said.

"He was a timid boy, who was having difficulty integrating, but he never displayed any violent attitudes," a local education official said.