Assistant Secretary-General for Human Rights Ivan Simonovic will spend four days in South Sudan starting Tuesday and will meet with senior government officials, a U.N. report said.
Thousands of people have died and an estimated 230,000 have been displaced in fighting that started in mid-December.
Simonovic will "look into cases of rights violations believed to have been committed by both sides in the conflict ... between pro- and anti-government forces," the report said.
The U.N. Mission in South Sudan has estimated that the number of people killed in the conflict that erupted Dec. 15 may be as high as 10,000.
Simonovic said there were growing concerns about the number of civilians being detained following house-to-house searches in the country.
Negotiations to end the South Dudan conflict are in progress in Ethiopia.
South Sudan became an independent country in 2011.