NASIR, South Sudan - Like many 13 year-olds, Gach Chuol is timid, shyly looking down at the ground as he speaks to a stranger.
But he is also joining South Sudan's war to avenge the death of his parents, and brandishes an AK-47 assault rifle as he recalls why he traded his school books for arms.
"I just want to fight because of what they have done to my parents," said Chuol, speaking at a rally organised by the White Army, a militia that took up arms again to fight government troops in South Sudan's four month-old civil war.
Brutal fighting has pitted President Salva Kiir's forces against those loosely allied with rebel chief Riek Machar, sacked as vice president in 2013.
The conflict has spread from the capital Juba to oil-rich states, with the rebels this week celebrating the recapture of the key town of Bentiu in a renewed rebel offensive they claim will seize crucial oil fields.
But it has also taken on an ethnic dimension, pitting Kiir's Dinka tribe against militia forces from Machar's Nuer people, and the scale of the fighting has led aid workers to warn of possible famine.
UN Secretary General Ban Ki-moon warned Wednesaday that "without immediate action, up to a million people could face famine in a matter of months".
However teenagers like 15-year-old Matt Thor, whose father was killed shortly after fighting broke out on December 15, are consumed by the desire for retribution.
"I want to go and kill," he said, holding a gun too big for his small frame. "I want to go to the place of war, because I want to fight with Dinka."