UN human rights chief Navi Pillay is heading to conflict-torn South Sudan after a wave of mass killings of civilians, her office said Friday.
"In the wake of the recent killings in Bentiu and Bor in South Sudan, the high commissioner is leaving for Juba," spokeswoman Cecil Pouilly told reporters, adding that Pillay would arrive Monday.
Pillay will carry out a joint mission with Adama Dieng, the UN's special envoy for the prevention of genocide.
Pouilly said Pillay and Dieng were being sent to South Sudan by UN chief Ban Ki-moon, as the world body steps up efforts to stem the conflict in the world's newest country.
The UN Security Council on Thursday brandished the threat of sanctions against South Sudan government forces and rebels responsible for escalating abuses.
Both sides have been implicated in atrocities and war crimes.
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 where they were sheltering.
The government of President Salva Kiir has been locked in battle for four months with rebels loyal to sacked vice president Riek Machar.
The 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.
Violence has also taken on an ethnic dimension, pitting Kiir's Dinka tribe against militia forces from Machar's Nuer people.