JUBA - The UN's top human rights official arrived in South Sudan on Monday, officials said, amid an increase in global concern over the country's civil war and a wave of atrocities.
A spokesman of the UN Mission in South Sudan (UNMISS), Joe Contreras, said High Commissioner for Human Rights Navi Pillay arrived in the capital Juba on a joint mission with Adama Dieng, the UN's special envoy for the prevention of genocide.
The two are expected to remain in the country for two days and investigate on behalf of UN chief Ban Ki-moon. They are expected to meet South Sudan's President Salva Kiir and other senior officials.
Last week the UN Security Council brandished the threat of sanctions against South Sudan government forces, loyal to President Kiir, and rebels behind former vice president Riek Machar, who are responsible for escalating abuses.
Both sides have been implicated in atrocities and war crimes including massacres, rape, attacks on UN bases sheltering civilians from ethnic violence and the recruitment of child soldiers.
Last week, the rebels were blamed for the killings of hundreds of people in the oil hub of Bentiu, and a pro-government mob killed dozens of civilians in an attack on a UN base in Bor.
Kiir's government has been fighting Machar's forces -- a mix of army defectors and ethnic militia -- since December 15.
The four-month-old war has left thousands and possibly tens of thousands of people dead, and forced over one million to flee their homes, sparking a massive humanitarian crisis.
More than 78,000 civilians are currently crammed into eight UN bases in the country, while more than a million people have been displaced within the country or have fled to neighbouring states, mainly Uganda and Ethiopia.
Violence has also taken on an ethnic dimension, pitting Kiir's Dinka tribe against militia forces from Machar's Nuer people.