A top South Sudanese military commander has defected and joined the largest rebel group fighting troops loyal to President Salva Kiir.
Lt Col Chan Garang, an ally of former army chief Paul Malong, defected with 200 soldiers, Reuters news agency reports.
The commander said that he had defected because Mr Malong's allies were being badly treated.
He added that troops had not been paid for seven months and other ethnic groups were being discriminated against.
"I left Juba because when are you are a supporter of Paul Malong, you will be arrested," he said.
President Kiir, Mr Malong and Lt Col Garang are ethnic Dinkas and any split within the powerful group could represent a threat to Mr Kiir.
Mr Malong who is under house arrest in the capital Juba was sacked in May.
UN investigators blame the former army chief of directing militias responsible for the rape, torture and murder of civilians.
Over the weekend, government troops surrounded his house in the capital and unsuccessfully attempted to disarm his bodyguards. An armed stand-off continues outside his house, Reuters reports.
Garang said he was preparing for an offensive: "We are preparing our army so that we can launch an attack on Juba. Salva Kiir divided the tribes so we need him to go."
Malong was unreachable by phone, but his wife Lucy Ayak distanced her husband from the defected commander.
"[If Garang] is not happy with the government and he has deserted. Why is he saying it is the issue of General Malong?," she asked Reuters.
The four-year civil war in South Sudan which broke out in 2013 has split the country along ethnic and regional lines.
A third of the population of 12 million have fled their homes and half are dependent on food aid.
