South Sudan army urges civilians to leave Bentiu
The BBC's Alastair Leithead says thousands are fleeing Bentiu
amid "fireballs and shells" as government forces approach
The army in South Sudan has told all
civilians to leave the city of Bentiu, saying it is about to recapture the oil
hub from rebel forces.
Military spokesman Philip Aguer told the BBC government forces were on the edge of the city, with only a bridge separating them from the centre.
The rebels have not commented.
UN peacekeeping chief Herve Ladsous says the conflict has killed "very substantially in excess" of 1,000 people since 15 December.
Thousands of people have already fled Bentiu, one of two main cities seized by rebel forces.
The BBC outlines the background to South Sudan's crisis - in 60
seconds.
Several thousand have sought refuge in a UN camp in the city, where people have been divided according to their ethnic group in order to prevent clashes between them.
The conflict has seen outbreaks of ethnic slaughter betweens Dinkas, the community of President Salva Kiir, and Nuers, like rebel leader Riek Machar.
Bentiu is the capital of the oil-rich Unity state. The fighting has seen South Sudan's oil output fall by about 20%.
South Sudan is the world's newest state. It became independent in 2011 after seceding from Sudan.
