Despite commitments to stop recruiting children under 18, government forces in South Sudan continue to actively recruit and use child soldiers, Human Rights Watch (HRW) said today.

According to HRW, boys as young as 13 are joining troops in Malakal, Upper Nile state, sometimes as a result of force. An estimated 12,000 children are thought to have been recruited to fight with armed groups on both sides of the conflict that has plagued South Sudan since its secession from the north in 2011.

It is a war crime to recruit and use children under the age of 15 as soldiers, yet HRW has collected accounts from dozens of young men and their families who have been forced to fight.

The SPLA, South Sudan's national army, signed an agreement forbidding under 18s from being recruited in August 2013, but resumed the practice when the latest wave of violence broke out in Juba, the capital city, in December of that year.

An attempted coup by soldiers loyal to President Salva Kiir's former deputy Riek Machar caused fighting to spread throughout the country, fracturing it along ethnic lines, though leaders in South Sudan have stressed that the war is political, not tribal. Described as the "most pressing humanitarian crisis in Africa", the violence has killed more than 10,000 people and displaced 1.9 million.

According to the UN, some children are voluntarily leaving the UN 'protection of civilian' site in Malakal to fight with government forces. Others, however, are being taken by force.

One young man told HRW researchers that he had been picked up along with six "small" children whom he thought were between 13 and 15 years old. They were driven to Koka, an area where violence had broken out.

"We were told to go to fight, given weapons, and attack together with other soldiers," he said. "We were given uniforms, almost immediately told to fight...all of us."

Both sides renewed a commitment to ending the use of child combatants in 2014. Machar signed a commitment with the UN special representative of the secretary-general for children in armed conflict to "take all measures to prevent grave violations against children immediately," in May 2014, and in June the government made a fresh commitment to having a "child-free army".

However, it appears neither is holding to their promise.

"South Sudanese children's lives are being devastated by conflict, with children once again going to war instead of to school," said Daniel Bekele, Africa director at Human Rights Watch.

"Both sides should stop recruiting children, and hold those responsible to account."

Despite these problems, a planned release of 3,000 child soldiers is currently being rolled out in South Sudan.

At the end of January, almost children surrendered their weapons and laid down their uniforms at the village of Gumuruk in eastern Jonglei State.