James Wani Igga appointed South Sudan vice-president
South Sudan President Salva Kiir has appointed James Wani Igga as his deputy, state radio has announced.
Mr Igga has been speaker of parliament and a commander in the Sudan People's Liberation Movement (SPLM), the ex-rebel group that now runs the country.
He succeeds Riek Machar, who was sacked by the president last month following an apparent power struggle.
South Sudan became independent in 2011 after decades of conflict with Sudan, making it the world's youngest country.
Numerous armed groups remain active in the oil-rich country.
After his dismissal, Mr Machar said he planned to challenge Mr Kiir for the leadership of the SPLM so that he can run for president in the 2015 election.
The entire cabinet was dismissed at the same time as Mr Machar on 24 July, and replaced this month with a smaller team.
Mr Kiir is from the Dinka community, which is the largest in South Sudan, while Mr Machar is from the second-largest group, the Nuer, some of whom have complained about Dinka domination.
Correspondents say Mr Kiir's choice of vice-president may be a way of shoring up support from Mr Igga's large Bari community in South Sudan's Central Equatoria region ahead of the elections in 2015.
Both Sudan and the South are reliant on their oil revenues, which account for 98% of South Sudan's budget. But the two countries cannot agree how to divide the oil wealth of the former united state. Some 75% of the oil lies in the South but all the pipelines run north. It is feared that disputes over oil could lead the two neighbours to return to war.
Although they were united for many years, the two Sudans were always very different. The great divide is visible even from space, as this Nasa satellite image shows. The northern states are a blanket of desert, broken only by the fertile Nile corridor. South Sudan is covered by green swathes of grassland, swamps and tropical forest.
Sudan's arid north is mainly home to Arabic-speaking Muslims. But in South Sudan there is no dominant culture. The Dinkas and the Nuers are the largest of more than 200 ethnic groups, each with its own languages and traditional beliefs, alongside Christianity and Islam.
The health inequalities in Sudan are illustrated by infant mortality rates. In South Sudan, one in 10 children die before their first birthday. Whereas in the more developed northern states, such as Gezira and White Nile, half of those children would be expected to survive.
The gulf in water resources between north and south is stark. In Khartoum, River Nile, and Gezira states, two-thirds of people have access to piped drinking water and pit latrines. In the south, boreholes and unprotected wells are the main drinking sources. More than 80% of southerners have no toilet facilities whatsoever.
Throughout the two Sudans, access to primary school education is strongly linked to household earnings. In the poorest parts of the south, less than 1% of children finish primary school. Whereas in the wealthier north, up to 50% of children complete primary level education.
Conflict and poverty are the main causes of food insecurity in both countries. In Sudan, many of the residents of war-affected Darfur and the border states of Blue Nile and South Kordofan, depend on food aid. The UN said about 2.8m people in South Sudan would require food aid in 2013. The northern states tend to be wealthier, more urbanised and less reliant on agriculture.