A South Sudanese military spokesperson reportedly questioned the credibility of a statement issued Wednesday by the Unicef, in which it alleged that at least 129 children were killed during clashes between government and rebel forces in May. According to the United Nations agency, an estimated 13,000 children have been recruited by various factions to participate in the protracted conflict in the world’s youngest nation.

“The violence against children in South Sudan has reached a new level of brutality,” Unicef Executive Director Anthony Lake said, in the statement. “Survivors report that boys have been castrated and left to bleed to death. Girls as young as 8 have been gang raped and murdered. …Children have been tied together before their attackers slit their throats. ...Others have been thrown into burning buildings.”

South Sudanese military spokesperson Col. Philip Aguer reportedly said that it was not in the nation's culture to commit such atrocities and called for a full investigation, adding that whoever was responsible must face justice.

Fighting in the world’s youngest nation broke out in December 2013 when President Salva Kiir accused former vice president Riek Machar of plotting a coup to overthrow the government. The ensuing political infighting later intensified into a full-fledged civil war between the rebel army, led by Machar, and government forces.

While the exact number of those killed since then is hard to estimate, the figure is believed to be over 10,000. An estimated 2 million have been internally displaced and nearly 4.6 million people are facing severe food insecurity in the impoverished nation. 

According to a recent report by the United Nations High Commissioner for Refugees (UNHCR), the total number of South Sudanese refugees -- who fled to the neighboring nations of Ethiopia, Kenya, Sudan and Uganda -- grew from 114,400 to 616,200 within a span of just 12 months in 2014.

“The neighboring countries are severely impacted by this massive outflow, and humanitarian agencies lack the resources to address the enormous and growing needs. With a refugee population that is comprised of 70 percent children, there is an even more urgent need to step up funding and address the most basic requirements for their protection,” UNHCR's António Guterres said, in a statement released earlier this week.

The violence in the country has also damaged its fledgling, oil-dependent economy -- 95 percent of the country's revenues come from oil exports -- which relies on the output of gas fields in the conflict-mired state of Unity, and the Upper Nile regions.

“In the name of humanity and common decency this violence against the innocent must stop,” Lake said, in the statement.