"WE WERE picked up at checkpoints or during house searches. They recognized us by our accents or by the traditional marks on our faces. 200-400 of us were brought to a room of a police station, so small that we were suffocating. Suddenly they opened fire on us from two windows. I fell to the ground, and was protected by the bodies of dead and injured lying on top of me. Some of the wounded were moaning, and they opened fire twice again during the night.” This is how a survivor described to me the killings at a police station in Gudele in Juba, South Sudan. He is just one of many victims of horrible crimes committed by all sides, whose only fault is to be from the wrong ethnicity.On 14 July 2011, South Sudan celebrated becoming the UN’s 193rd and newest member state, after decades of fighting for independence during which 2.5 million South Sudanese lost their lives.But today, a power struggle between its President Salva Kiir (ethnic Dinka) and former Vice-President Riek Machar (ethnic Nuer) has degenerated into an increasingly ethnically driven armed conflict.So far, thousands have been killed during fighting and in inter-ethnic attacks on Nuer and Dinka civilians. Hundreds of thousands have been displaced and are looking for a safe haven. There are credible reports of mass and extrajudicial killings, enforced disappearances, sexual violence, looting, arson and wanton destruction of property as well as the use of children as "soldiers.” Who started this conflict? And who is targeting civilians? The "truth” depends on what ethnic background you have. When I talked to displaced people, victims and their families in camps in Juba, Bentiu and Bor, I found their perception of the conflict so influenced by their ethnic affiliation that it was as if they lived in different realities.In such a situation, it is imperative that the UN monitors and publicly reports on human rights violations, victims and perpetrators. Only impartially established facts will prevent false rumours from further fuelling the conflict, help to settle grievances and bring accountability in the long term. South Sudan has a tradition of impunity. There was never any accountability for crimes committed during the previous major conflict involving the same two ethnic groups in 1991. This has contributed to history tragically repeating itself.  It is thus very encouraging that the African Union Peace and Security Council has decided to establish an international commission of inquiry on causes of the conflict and the crimes that have been committed. To protect civilians from the violence, and learning from the tragedies of Rwanda and Srebrenica, the UN is trying to help its newest member in an unprecedented way: the United Nations Mission in South Sudan has opened the doors to its premises to provide protection to about 70,000 people who fear for their lives because of their ethnicity.It is a huge challenge to provide them with food, health care, water and sanitation. I saw a hospital without any medication in Bentiu, people surviving with very limited water supplies in Bor, and 20,000 displaced squeezed into a space amounting to only four square meters per person in a camp in Juba.But the toughest challenge of all is to protect them physically: a small UN compound in Akobo was stormed by armed youths who killed 20 civilians, and also two Indian UN peacekeepers who were trying to protect them. The UN’s peacekeeping force in South Sudan desperately needs to be strengthened and become more robust."One month of fighting has set South Sudan back a decade,” a development expert told me in Juba. Development statistics illustrate how tough life is: half the population lives in poverty and is malnourished. A young woman is as likely to die giving birth as she is to finish primary education. One in every ten children dies before his or her fifth birthday.Yet, South Sudan can become stable and prosperous. It is a country rich in oil, which amounts to two-thirds of its GDP. Instead of being wasted on mismanagement, corruption and conflict, revenue should be used for social development.The window of opportunity is now. The UN should do everything it can to protect the people of South Sudan and support efforts to stop the war and ensure sustainable peace. The people of South Sudan deserve a better future. The oil will not last forever.The writer is the United Nations Assistant Secretary-General for Human Rights