UNITED NATIONS — Civilians in South Sudan have been the main target of recent ethnic violence that likely killed thousands and subjected thousands more to rape, arbitrary arrest, torture and the looting and burning of their homes, the United Nations said Friday in its first report on human rights abuses during the conflict.The U.N. peacekeeping mission in South Sudan said the report on the progress of human rights investigations during the first six weeks of the crisis, from Dec. 15 through Jan. 31, offers a "snapshot" of the violence perpetrated mainly by forces loyal to President Salva Kiir, who is an ethnic Dinka, and rebel soldiers loyal to dismissed former vice president Riek Machar, who is an ethnic Nuer.During more than 500 interviews, the report said, "witnesses, victims and government and security officials reported the deliberate targeting of civilians, both nationals and foreigners, in extrajudicial and other unlawful killings, including mass killings, enforced disappearances, gender-based violence such as rapes and gang rapes, and instances of ill-treatment and torture by forces from both sides of the conflict."Since incidents are still being investigated, the mission's human rights experts said "it is premature to judge whether or not sexual violence was used as a weapon of war."The interim report focuses on alleged rights abuses in the four states which have seen the heaviest fighting — Central Equatoria where the violence began in the capital Juba on Dec. 15, and Jonglei and oil-rich Unity and Upper Nile states where it quickly spread in the following days.The government insists that the unrest was sparked by a failed military coup mounted by soldiers loyal to Machar. The ousted vice president denies the coup allegation but says his goal is to have Kiir removed from power.While the trigger for the violence remains in dispute, the report said it has led to "a major security, human rights, and humanitarian catastrophe," and increased ethnic polarization in the world's newest nation.The report doesn't cover events in February but it said the situation on the ground is still volatile, and violations of human rights are continuing, especially in areas where there is continued fighting.The U.N. mission, in a release accompanying the report, said that in the recent battle for control of Malakal, the capital of Upper Nile State, there was fresh evidence of rights abuses including the extra-judicial execution of two children outside the perimeter of the U.N. compound on Thursday.A U.N. patrol also collected eyewitness testimony from residents alleging that opposition forces targeted and killed 10 unarmed civilians at the Malakal Teaching Hospital on the basis of their ethnic background on Wednesday.During the first six weeks of the conflict, the report said, "it is clear that civilians bore the brunt of much of the fighting and that gross violations of human rights were committed."The U.N. said that in Juba credible witness accounts indicate that soldiers from South Sudan's military, known as the SPLA, reportedly of Dinka origin, deliberately targeted and killed Nuer civilians after house-to-house searches.In one incident on Dec. 16, it said SPLA soldiers arrested 38 civilians of Nuer origin, reportedly tied them together in a line, forced them to walk and then untied some, told them to run and shot them."As of Jan. 31, attacks against civilians of Nuer origin in Juba continued," the report said. "SPLA soldiers and heavily armed civilians were reportedly still conducting house-to-house searches for Nuers, who were also targeted on their way to and from safe havens."In Jonglei State, where the capital Bor changed hands three times, the U.N. said information it collected indicates that serious human rights violations were committed by various actors belonging to both government and opposition forces."Violations seem to have affected the most vulnerable — the elderly, injured, disabled, and individuals otherwise unable to escape," the report said.The mission's human rights experts said they are investigating the Dec. 19 attack on a U.N. base which was overrun and ransacked by about 2,000 Nuer youth and security forces personnel who had defected. They said about 27 Dinkas who had sought protection there were killed.The rights experts said they are also investigating a reported mass killing at the residential area of St. Andrew's Church compound in Bor where many civilians sought refuge and eight to 12 Dinka women — some belonging to the clergy — were reportedly killed in the chapel, allegedly by opposition forces.In Unity State, the report said, U.N. rights experts have received reports of at least seven mass graves and believe at least 230 civilians — Dinkas and Nuers including women and children — were killed on ethnic grounds in Rubkona, Bentiu, the Unity oil fields and Tharjath between Dec. 16 and Jan. 31.The report said interviews with victims also indicate that women — mostly foreigners including Kenyans, Ugandans, Ethiopians and Eritreans — were subjected to sexual violence in Rubkona and Bentiu. The human rights experts said they received reports that at least a dozen women were reportedly gang raped between Dec. 17-27, allegedly by opposition forces.