African Union (AU) experts in South Sudan say thousands of children have been killed or abducted since fighting erupted in the war-ravaged nation eight months ago.

"The present conflict can be characterized as nothing less than a war on the children of South Sudan," said Julia Sloth-Nielsen, who heads an AU committee investigating child rights in the country, on Friday.

The committee has launched an investigation into the mass slaughtering of displaced children.

Over 900 children have been kidnapped and forced to fight as soldiers in the state of Jonglei, the committee said.

"We have received numerous reports of children -- even babies -- being wantonly killed," Sloth-Nielsen stated, adding that the assaults on children are "perilously close to constituting a crime against humanity."

South Sudan plunged into violence in December 2013, when fighting erupted between troops loyal to President Salva Kiir and defectors led by his former deputy Riek Machar around the capital Juba.

The conflict soon turned into an all-out war between the army and defectors, with the violence taking on an ethnic dimension that pitted the president’s Dinka tribe against Machar’s Nuer ethnic group.

The clashes left thousands of South Sudanese dead and forced around 1.5 million people to flee their homes in the world’s youngest nation.

The widespread displacement has contributed to mass hunger and food shortages. Aid workers warn of famine if fighting continues.

South Sudan gained independence in July 2011 after its people overwhelmingly voted in a referendum for a split from the North.