11,000 children in the Democratic Republic of Congo are in the hands of armed groups or unaccounted for, says Amnesty International
Three years after the end of a war in which they were forced to fight, many children have not been demobilised, says the human rights group.
It blames a lack of political will, poor organisation and corruption.
The five-year conflict triggered a humanitarian crisis estimated to have killed nearly four million people.
A demobilisation and reintegration (DDR) programme launched two years ago was aimed at releasing an estimated 30,000 child soldiers and getting them back into civilian life.
But Amnesty says the programme is failing, and is appealing to the winner of forthcoming presidential elections to make the issue a priority.
"The new government must make it their first priority to ensure that all children associated with armed forces and groups are released, protected and provided with meaningful educational and income-generating opportunities to enable them to stay within their communities," the report says.
"This is the only way to prevent the re-recruitment and further abandonment of these children."
The report says young girls are being disproportionately affected, used as sex slaves by military commanders or regarded as dependents of adult fighters.
Girls made up 40% of the children taken by armed groups during the war yet the vast majority remain unaccounted for, Amnesty says.
"A lot of them were used more as sex slaves and therefore the combatants are considering them as their possession or their wife," Amnesty researcher Veronique Albert told the BBC.
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