JOHANNESBURG - The United Nations on Monday condemned ethnic killings by South Sudan rebels that left hundreds of people dead last week after the fall of an oil town to the opposition forces.

The world body said the killings took place in Bentiu, the hub of the country's main oil producing region in the north.

U.N. spokesman Joe Contreras said in a statement that some members of the rebel Sudan Peoples' Liberation Movement in Opposition broadcast hate messages on radio after taking control of Bentiu, urging certain ethnic groups to leave town.

Some commanders from the Nuer people called on their men to rape non-Nuer women in revenge attacks. Other commanders urged unity and an end to tribalism, but their messages failed to halt the violence.

The governing Sudan Peoples' Liberation Movement and the army split in December between supporters of President Salva Kiir, a member of the Dinka people, and his rival, Vice President Riek Machar, a Nuer. The power struggle triggered fighting and ethnic killings in many parts of the country, especially in towns such as Bor and Malakal that have changed hands multiple times.

Peace talks in neighboring Ethiopia produced a truce in January that has not stopped the fighting.

Contreras said U.N. human-rights investigators had established that after the SPLM in Opposition took Bentiu in Unity state last week, its predominantly Nuer fighters searched a mosque, hospital, and other areas where people had taken refuge and killed people on the basis of ethnicity and nationality. A day later, armed Dinka youths invaded a U.N. peacekeeping base in the Jonglei state town of Bor and opened fire, killing dozens of Nuer.

"At Bentiu Hospital, on 15 April, several Nuer men, women and children were killed for hiding and declining to join other Nuers who had gone out to cheer the [rebel] forces as they entered the town," Contreras said. "Individuals from other South Sudanese communities, as well as Darfuris, were specifically targeted and killed at the hospital."

The Nuer rebels also entered the Kalli-Ballee mosque where hundreds of civilians were sheltering, allowing some people to go, based on ethnicity, but detaining and killing others. More than 200 people were killed and 400 were injured at the mosque, the U.N. said.

U.N. peacekeeping forces rescued about 500 people from the hospital, mosque, and other locations and escorted them to their base.