Two Argentinian brothers, ages seven and nine, told psychiatrists they slowly tortured a two-year-old girl to death - in a revelation that could scrap a law prohibiting the prosecution of minors.

Judge Marta Pascual said the children confessed to killing neighbour Milagros Belizan in a shantytown south of the capital.

"They understood her pain but it did not move them," said Ms Pascual, a youth judge for Buenos Aires' Lomas de Zomara district. "In some form it gave them pleasure."

Milagros disappeared from her home in the Almirante Brown neighbourhood on Sunday. Her family found her body in a vacant lot 10 blocks away.

She had been stripped naked, beaten and strangled with telephone cord that was left around her neck. The discovery prompted neighbours to attack an adult suspected of the crime before the two boys confessed.

Argentinian law prohibits the prosecution of anyone under 18 years old. Instead, such juveniles are generally held in youth homes until they reach 18, when they are released without further punishment.

The murder has many Argentines calling for stiffer punishments - including prosecuting them once they come of age.

"There's the idea among Argentine lawyers, psychologists and sociologists that the child is always the victim and can never be the victimiser," constitutional lawyer Gregorio Badeni said.

"But if it were up to the people in the shantytown where that girl was murdered, they would kill the two boys."

Other Argentinians disagreed that child killers should be tried like adults.

"These two boys are victims just like the poor girl they killed," family psychologist Cristina Castillo said.