South Sudan Fighters Carried Out a 'Month of Rape': UN

South Sudanese fighters carried out a "month of rape", a top United Nations rights chief has said, warning that atrocities continue with a seventh ceasefire broken.

"Violations continue to take place," said UN Secretary-General for Human Rights Ivan Simonovic, after visiting the "destroyed" towns of Bentiu and Malakal.

Simonovic, speaking after visiting areas that have seen some of the worst fighting in the past 13 months of war, said he had received the "simply appalling" report of fighters embarking on a campaign of rape.

"This is absolutely intolerable," he said, without giving further details as to which of the multiple armed forces was responsible.

"It is essential to push for peace, this situation is not sustainable," he added, in a statement released Friday.

Fighting erupted in South Sudan, the world's youngest nation, in December 2013 when President Salva Kiir accused ousted deputy Riek Machar of attempting a coup.

It quickly spread from the capital Juba, triggering a cycle of retaliatory massacres across the country.

UN chief Ban Ki-moon this week accused the leaders of putting their own interests above those of their people, after they agreed another ceasefire on Sunday but failed to reach a power-sharing deal.

Kiir and Machar have been set a March 5 deadline to strike a final full peace agreement, but similar previous deadlines have been repeatedly ignored.

UN aid chief Valerie Amos arrives in South Sudan Friday for a three-day assessment mission.

Half the country's 12 million people need aid, according to the United Nations, which is also guarding some 100,000 civilians trapped inside UN camps ringed with barbed wire, too terrified to venture out for fear of being killed.

Simonovic also repeated calls for the African Union to release findings of its inquiry into atrocities, amid warnings that ignoring its recommendations would help the guilty to evade justice.

"Peace, if it is to be sustainable, needs to include justice," Simonivic said.