Mass graves fuel fears of ethnic bloodshed in South Sudan Nairobi, Kenya: Amid the eruption of violence along ethnic lines in South Sudan, UN investigators discovered a mass grave in a rebel-held city, the United Nations said on Tuesday as a possible opening occurred for negotiations to avert civil war in the world's newest country. The bodies were found in Bentiu: one grave with 14 bodies and a site nearby with 20 bodies, said UN human rights office spokeswoman Ravina Shamdasani. there is a palpable fear among civilians of both Dinka and Nuer backgrounds that they will be killed on the basis of their ethnicity The government 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 Shamdasani, referring to government military forces. South Sudan President Salva Kiir is Dinka while Machar is Nuer. US Secretary of State John Kerry spoke on the phone on Tuesday with Machar, who said he told Kerry he is ready for talks with Kiir, likely to take place in Ethiopia. "I will form a high-level delegation, to which I will give full power to negotiate an accord," Machar told Radio France Internationale. We want Salva Kiir to quit power. We want a democratic nation and free and fair elections. Violence began spreading across South Sudan after a fight among Kiir's presidential guards late December 15, pitting Nuer against Dinka. Some 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, UN human rights chief Navi Pillay said. The UN Security Council approved plans on Tuesday to almost double the number of UN peacekeepers in South Sudan from 7000 to 12,500 following a call by Secretary-General Ban Ki-moon for more UN force. UN staff visited the mass grave in Bentiu on Monday. Originally the UN said 75 bodies had been seen but later corrected that statement to 34 bodies seen and 75 people missing and feared dead. The United States, Norway and Ethiopia are leading efforts to open peace talks on the 10-day-old crisis. Officials say Kiir and Machar have agreed to meet but specifics including the status of 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 Machar, said military spokesman Colonel Philip Aguer. The military said armed elements have entered a UN refugee camp in Bor, a frightening situation for the 17,000 civilians seeking refuge there. Government troops will also soon advance on Bentiu, in oil-rich Unity state, he said. The UN has staff in the country investigating mass killings, said Pillay. It is unclear who is responsible for the deaths, she said. Two other mass graves were reportedly found in Jebel-Kujur and Newside, near Eden, she said. The country's top UN humanitarian official said Monday that he believes the death toll from 10 days of violence has surpassed 1000 but added that there are no firm counts. The official, Toby Lanzer, estimated that there are more than 100,000 internal refugees across the country seeking shelter from the violence. A top European Union official, Catherine Ashton, said political dialogue must include all groups, including those whose leaders are currently imprisoned. The use of force, she said, will achieve nothing. I am extremely concerned that South Sudan risks spiralling into a disaster for both its own people and the region. Such a situation can, and must, be avoided," Ashton 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.that he enter negotiations without preconditions.