WASHINGTON : US lawmakers are pressing Washington to get tough on institutionalised sexual slavery of boys by Afghan forces, with some invoking a human rights law that prohibits American aid to foreign military units committing such violations. The revelation prompted congressman Duncan Hunter to demand US Defence Secretary Ashton Carter take "immediate steps to stop child rape" amid an American military presence in Afghanistan.

The Department of Defence replied to Hunter last week, stating in a letter seen by AFP that it was committed to holding perpetrators accountable.

The letter added that General John Nicholson, the US commander in Afghanistan, had "reaffirmed" tactical guidance "stating that when US personnel suspect members of (Afghan security forces) have violated human rights, including child sexual abuse, they must report that... to appropriate (Afghan) officials".

The response falls far short of a zero tolerance policy, Hunter said.

"At the very least, the US government should state, as a position of official policy, that child rape amid a US force presence won't be tolerated and expectations should be imposed on how allegations and evidence are handled," he told AFP this week. "So far that's yet to occur beyond a simple reporting requirement."