The United Nations says South Sudan may plunge into a widespread ethnic conflict that could affect the stability of the whole region.
Yasmin Sooka, the head of a team of UN human rights investigators, made the remarks during a briefing to the UN Human Rights Council on Wednesday.
South Sudan is "on the brink of an all-out ethnic civil war, which could destabilize the entire region," Sooka said.
She said a recent visit by the UN team of investigators found indications that "a steady process of ethnic cleansing is already underway in some parts of the country."
The UN official added that thousands of women had been raped during the conflict across the country. She described South Sudan as a country where children as young as two years of age had been raped.
Elsewhere in the briefing, Sooka said the conflict had also badly damaged the country's economy. South Sudan had the world's highest inflation rate, at more than 800 percent in October.
The UN official warned that fighting was expected to "begin in earnest" now that the dry season has arrived in South Sudan.
Zeid Ra'ad Zeid al-Hussein, the UN high commissioner for human rights, has urged the human rights council to call on South Sudan's leaders to refrain from incitement to ethnic hatred and violence.
He said "there may still be some space for consequential action to pull the country back from a worst-case scenario."
Zeid also stated that when local leaders intervened recently to halt hate speeches, threats of violence decreased.
In an address to parliament on Wednesday, South Sudan's President Salva Kiir urged an end to expressions of ethnic hatred. "I am calling upon all of you to forgive one another." He also called for national dialogue.
The South Sudanese president again called for a ceasefire. He, however, did not offer much detail on how a truce would work with multiple opposition groups across the country.
South Sudan gained independence in July 2011, but descended into war in December 2013, after President Kiir accused the former vice president, Riek Machar, of plotting a coup.
Numerous international attempts to reach a truce between the warring sides have failed.