UNITED NATIONS - Rebels slaughtered hundreds of civilians when they seized the South Sudan oil hub of Bentiu, hunting down men, women and children who had sought refuge in a hospital, mosque and Catholic church, the United Nations said on Monday.Rebel troops overran Bentiu, the capital of the oil producing Unity State, on Tuesday. More than 1 million people have fled their homes since fighting erupted in the world's youngest country in December between troops backing President Salva Kiir and soldiers loyal to his sacked vice president, Riek Machar.The fighting has exacerbated ethnic tensions between Kiir's Dinka people and Machar's Nuer.The UN peacekeeping mission in South Sudan said that its human rights investigators confirmed that rebels "searched a number of places where hundreds of South Sudanese and foreign civilians had taken refuge and killed hundreds of the civilians after determining their ethnicity or nationality."The UN mission, known as UNMISS, strongly condemned the targeted killings on April 15-16 and the use of Radio Bentiu FM to broadcast hate speech.While some rebel commanders broadcast calls for unity, "others broadcast hate messages declaring that certain ethnic groups should not stay in Bentiu and even calling on men from one community to commit vengeful sexual violence against women from another community," UNMISS said in a statement.At Bentiu hospital, Nuer men, women and children were killed for hiding and not joining other Nuers in cheering the rebels as they entered the town. People from other South Sudanese communities and from Darfur in Sudan were also targeted and killed, the United Nations said.Rebels also entered the Kali-Ballee Mosque, a Catholic church and an empty World Food Program compound where civilians had sought refuge and separated them by nationalities and ethnicities - escorting some to safety and killing others."More than 200 civilians were reportedly killed and over 400 wounded at the mosque," the UN mission said.