Hundreds of people have been killed in South Sudan after rebels seized the oil hub of Bentiu last week, the UN has said.

The victims, members of the Nuer ethnic group, were targeted at a mosque, a church and a hospital, the UN Mission in South Sudan said in a statement.

It added that the violence was encouraged by speeches broadcast on local radio stations, saying certain groups should leave the town and urging men to rape women.

Members of the Nuer community are seen as supporters of rebel leader, Riek Machar, while the South Sudan president, Salva Kiir, is a member of the country's largest group, the Dinka.

Although both men have prominent supporters from various communities, there have been numerous reports of rebels killing ethnic Dinkas and the army targeting Nuers since the conflict broke out in December 2013.

A ceasefire was signed in January but there has been a recent upsurge in fighting.

Last week, an attack on a UN base in the central town of Bor saw at least 58 people killed and could constitute a war crime.