Rebels in South Sudan have slaughtered at least 353 civilians in April last year, including people sheltering in a mosque, hospital and a United Nations base, U.N. rights investigators said Friday. The report is the first detailed account of two incidents that have highlighted a pattern of gross abuses and atrocities committed during the year-old civil war in the world’s youngest nation. The U.N. also noted that nearly nine months after the events, “no perpetrator has been held accountable” for the killings. In the 15 April 2014 attack on the northern oil-town of Bentiu, fighters backing South Sudan rebel leader Riek Machar murdered at least 287 civilians sheltering in a mosque, many of them traders and their families from neighbouring Sudan’s Darfur region. Later that day, 19 civilians were killed in the town’s hospital, U.N. investigators said. Fighters also took to the radio urging rival groups to be forced from the town and for men to rape women from the rival tribe. “Victims were deliberately targeted on the basis of their ethnicity, nationality or perceived support for one of the parties to the conflict,” the U.N. said in a 33-page report. Two days later on 17 April, in the eastern town of Bor, a gang of heavily-armed men marched on the U.N. base, where hundreds of civilians had fled to for protection. The “mob forcibly entered the protection site and went on a rampage of killing, looting and abductions”, the report by the U.N. peacekeeping mission in South Sudan, UNMISS said, adding the assault left at least 47 dead and was likely to have been “planned in advance.” The attack on Bentiu and the U.N. base in Bor are two of the most high profile massacres in a long list of atrocities carried out in the more than a year-long civil war. At least 353 civilians were killed and another 250 were wounded in the two attacks, the U.N. said. No overall death toll for the war has been kept, either by the government, rebels or the United Nations, although the International Crisis Group says it estimates that at least 50,000 people have been killed. Some diplomats suggest it could be double that figure, while hunger and disease have killed thousands more. Fighting broke out in South Sudan, the world’s youngest nation, in December 2013 when President Kiir accused his sacked deputy Riek Machar of attempting a coup. The fighting in the capital Juba set off a cycle of retaliatory massacres across the country, pushing it to the brink of famine. Both government forces loyal to Kiir and rebels loyal to Machar continue to fight, despite numerous ceasefire deals.