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South Sudan President Salva Kiir named veteran ex-rebel commander James Wani Igga to be his deputy Friday, succeeding the controversial former vice-president Riek Machar, state radio said.

Igga, Speaker of South Sudan's Legislative Assembly since 2005, appears a choice to balance ethnic diversity among leaders of the young nation and to shore up support ahead of elections due in 2015.

Deputy chairman of the ruling Sudan People's Liberation Movement (SPLM), Igga comes from the Bari tribe, whose homeland surrounds the capital Juba.

Last month Kiir took the surprise move of sacking the entire cabinet as well as Machar, a charismatic but controversial leader who fought on both sides of Sudan's brutal 1983-2005 civil war.

The purge initially created fears of reopening civil war splits between the majority Dinka people of Kiir and the Nuer tribe of Machar, but the fledgling nation reacted calmly.

However, Igga's appointment is seen as a way for Kiir to stem critics who argue too much power has been concentrated in the Dinka people, and to reach out to citizens in the Equatoria region in the southern half of the country where Igga is from.

"In the case of the tensions within the SPLM, there are immediate concerns about a repeat of the historical split between the Dinka and the Nuer," the United States Institute of Peace said in a recent report.

As speaker, it was Igga's honour to read out South Sudan's proclamation of independence in July 2011, following a referendum to split from Sudan set up by the 2005 peace deal that ended the war.

It is not clear who will succeed Igga in the important post of speaker.

These days smartly dressed in well cut suits and colourful ties, Igga is a veteran of the rebel force that fought Khartoum in the more than two decades long civil war.

Igga, 64, a Roman Catholic, grew up during Sudan's first north-south civil war, an on-off conflict that stretched from independence from Britain in 1956 to a 1972 peace deal.

But Igga was first drawn into politics defending rights of South Sudanese outside the country, while studying economics in the Egyptian capital Cairo.

Returning to Sudan he joined the rebels in 1985, two years after the rebellion began. He received military training in Ethiopia and Cuba and rose swiftly as a commander, retiring active service as a general in 2005 to enter politics.

With many of the early rebel commanders coming from the Dinka and Nuer people, Igga played a key role in persuading the people of the Equatoria regions -- fertile regions bordering Uganda, Democratic Republic of Congo and Kenya -- to support the fight.

When the rebels splintered along ethnic and ideological lines after Machar and other plotters tried unsuccessfully to topple rebel chief John Garang in 1991, Igga remained loyal to the mainstream force, mobilising the many tribes in the Equatoria region.

While Igga's appointment must still be ratified by a two-thirds vote in parliament, the SPLM holds the majority of seats and his appointment is expected to pass easily.