Dozens of children have been killed, at least 12 raped and others abducted and recruited in attacks in South Sudan's Unity state over a two-week period, the U.N. children's agency reported Monday.
Witnesses believe the attacks were carried out by armed groups aligned with South Sudan's military, UNICEF said in a statement Monday.
"Survivors reported to UNICEF staff that whole villages were burned to the ground by armed groups, while large numbers of girls and women were taken outside to be raped and killed - including children as young as seven," the statement said. "At least 19 boys - some as young as 10 years of age - and seven girls were killed. Others were mutilated or recruited to join the fighting and take care of stolen cattle."
South Sudan's military recently launched an offensive against rebel forces, drawing concern from watchdog groups and the regional monitoring bloc over fighting in Bentiu, the capital of Unity state.
Fighting is also taking place in the Upper Nile state.
Doctors Without Borders reported Sunday that health workers had fled with their patients into swamps as clashes hit the rebel stronghold of Leer in Unity state.
The International Committee of the Red Cross warned Monday that tens of thousands of people forced to flee fighting will suffer from a lack of food and health care while on the run.
"How many times will South Sudanese civilians be forced to flee a town under attack, knowing that if they don't their lives will be in danger?" Franz Rauchenstein, head of the ICRC delegation in South Sudan, said a statement. "We again ask of those involved in the fighting to not target civilians and let those trying to escape hostilities travel unimpeded."
The U.N. Security Council on Sunday condemned the renewed fighting.
South Sudan is an ethnically and linguistically diverse country with three large ethnic groups (Nuer, Dinka and Shilluk).
Unlike its Muslim northern neighbour, Sudan, people in South Sudan are mostly followers of traditional religions.
The world's newest state, which declared independence from Sudan in 2011, was plunged into conflict nearly 18 months ago between forces loyal to President Salva Kiir and rebels allied with his former deputy, Riek Machar.