Mass graves have been discovered in a rebel-held South Sudan city amid the eruption of ethnic violence that threatens to turn into civil war.
One grave in Bentiu had 14 bodies and another nearby 20 bodies, said the UN human rights office.
South Sudan minister of information Michael Makuei Lueth said Bentiu is under the control of rebels loyal to the country's former vice president, Riek Machar, indicating they were responsible for the killings.
The dead reportedly were ethnic Dinka who belonged to the Sudan People's Liberation Army, said the UN, referring to government military forces. South Sudan president Salva Kiir is Dinka while Mr Machar is Nuer.
Violence began spreading across South Sudan after a fight among Kiir's presidential guards 10 days ago pitting Nuer against Dinka.
Around 20,000 people seeking safety have crowded round the UN base in Juba, the capital, where at least two other mass graves are reported to have been found.
The United States, Norway and Ethiopia are leading efforts to open peace talks on the 10-day-old crisis. Officials say Mr Kiir and Mr Machar have agreed to meet but specifics including the status of Mr Machar's imprisoned compatriots are holding up talks.
South Sudanese troops, meanwhile, are advancing on Bor in order to take it back from troops loyal to Mr Machar, said a military spokesman.
The UN believes the death toll from 10 days of violence has surpassed 1,000 but added that there were no firm counts.
"I am extremely concerned that South Sudan risks spiraling into a disaster for both its own people and the region. Such a situation can, and must, be avoided," she said, adding: "The people of South Sudan have suffered war for too long to be plunged once more into an avoidable conflict."
South Sudan, the world's newest country, peacefully broke away from Sudan in 2011 following a 2005 peace deal. Before that, the south fought decades of war with Sudan. The country, one of the world's least developed, still has pockets of rebel resistance and sees cyclical, tribal clashes that result in hundreds of deaths.