The government has denied reports of recruiting child soldiers.
Human Rights Watch says children are being enlisted in the army in Malakal, in Upper Nile State.
In a report released today, the rights group says that the government forcibly recruited at least 15 children in recent weeks, and some willingly left the UN camp to join the government forces in the area.
But the government says this is not true.
The Minister of Information, Michael Makuei Lueth, says the government cannot recruit child soldiers because there are many adults who want to join the army.
He says the report of the Human Rights Watch is aimed at apportioning blame to both warring parties.
“How can we recruit child soldiers when we have sufficient man power? There are people who are above ages who want to be recruited because after this it is no longer a voluntary army, it is a paid army .How can you recruit a child so that you come and pay him” He said.
The United Nations says about 12,000 children are still serving in armed forces in South Sudan.
Human Rights Watch also said the SPLM in Opposition forces used child soldiers in battles in the past months. The SPLM in Opposition had earlier denied.