By Jeremy McDermott BBC correspondent in Colombia

The international non-governmental organisation Human Rights Watch has released a study on the use of child soldiers in Colombia, with levels among the highest in the world.

It says there are some 11,000 child soldiers fighting in Colombia's 39-year civil conflict and called upon all sides to make demobilisation of children a priority.

About a quarter of child soldiers are female

In a booklet entitled You'll Learn Not to Cry: Child Combatants in Colombia, Human Rights Watch has conducted a serious study of the problem of child soldiers in Colombia.

Some 112 former child combatants were interviewed for the publication, which describes how children are recruited into the ranks of the Marxist guerrillas and right-wing paramilitaries from as young as eight years old and gradually hardened to violence.

Around 25% of guerrilla ranks are female and the study highlighted the problem of sexual abuse many young girls are subjected to by their guerrilla superiors.

Females as young as 12 are forced to use contraception and, if they get pregnant, must undergo abortions.

The Colombian Government does have a special programme for children who are captured or desert the ranks of the warring factions.

In a safe house in Bogota, they are introduced to the childhood they never had and reintegrated into civil society.

The report demands that the warring factions halt the recruitment of children, but its call is likely to be ignored, particularly by the left-wing guerrillas, who make it a policy to recruit children and indoctrinate them with their Marxist ideals.