Dozens of children have been killed in fighting in South Sudan, where battles rage despite political deals to end almost two years of civil war, the United Nations has said.

The UN said that fighting in the northern battleground state of Unity has "intensified with grave consequences for civilians" in recent weeks, adding that 40,000 people are also starving to death.

The report by the UN Office for the Coordination of Humanitarian Affairs (OCHA) released late Friday detailed killings in just one area of Unity state during a two-week period.

It said that in the Leer district of southern Unity, which has swapped hands multiple times between government and rebel forces, at least 80 civilians were killed between October 4 to 22.

Almost three-quarters of those killed were children -- at least 57 killed in Leer -- while there were more than 50 cases of rape being used as "a weapon of war", the report said.

Both sides are accused of having perpetrated ethnic massacres, recruited and killed children and carried out widespread rape, torture and forced displacement of populations to "cleanse" areas of their opponents.

Hunger experts from the Integrated Food Security Phase Classification (IPC) have warned of a "concrete risk of famine" before the end of the year if fighting continues and aid does not reach the hardest-hit areas.

While some aid has reached two districts in Unity -- Buaw and Koch -- other areas are cut off.

Some 3.9 million people are in critical need of aid -- a third of the country's population and a massive 80 percent rise compared to the same period last year, the UN said.

Civil war began in December 2013 when President Salva Kiir accused his former deputy Riek Machar of planning a coup, setting off a cycle of retaliatory killings that have split the poverty-stricken, landlocked country along ethnic lines.

The army and rebels have repeatedly accused each other of breaking an internationally-brokered August 26 ceasefire, the eighth such agreement aimed at ending the nearly two-year long war.

Source: AFP