JUBA — South Sudanese President Salva Kiir has clipped the powers of his deputy Riek Machar, officials said Tuesday, a move that could raise ethnic tensions within the fragile and war-ravaged nation.

A presidential decree ordered "the withdrawal of all duly delegated powers assigned to the vice president" Riek Machar, a former guerrilla commander and an influential leader of the Nuer people, the country's second largest ethnic group.

Machar will be restricted to "discharge only his powers as stipulated" under the county's draft constitution, the order added. That includes acting for the president when he is out of the country, and membership of the cabinet and national security council.

Machar, a Dok Nuer from the key oil producing Unity state, is a controversial figure for many in South Sudan, but commands much loyalty among the Nuer, who make up much of the new nation's army.

During Sudan's 1983-2005 civil war that led to a peace deal paving the way for a referendum on South Sudan's independence, Machar fought on both sides of the conflict.

His Nuer faction split the South's then-rebel Sudan People's Liberation Army (SPLA) to side with Khartoum, battling troops commanded by Kiir from the mainly Dinka people.

His troops are accused of a brutal massacre in the ethnic Dinka town of Bor in 1991.

He later switched sides again, and was instrumental in bringing key militia forces back to the SPLA, but has long been distrusted by the majority Dinka people, who hold key military and government positions.

South Sudan is riven by ethnic tensions, with the military struggling to control rebellions and mend a society torn apart by one of Africa's longest-running wars, in which Khartoum pitted different southern militia forces against one another.

The presidential order has also suspended efforts led by Machar for "national reconciliation" aimed to bring together the war-weary nation, but which were seen by some as a means to boost his political standing.

Machar is seen as the top Nuer leader, especially after the death last August of the army's deputy commander Paulino Matip, a former Nuer rebel warlord, who also fought on both sides of the conflict. — AFP