Kiir said in a decree on state television Monday that he took the decision based on the powers given to him under the agreement on the resolution of conflict in the country.

The decision to sack Machar, Kiir said, was informed by recommendations of the ex-rebel group after Machar failed to heed his 48-hour ultimatum to return to the capital, Juba.

Machar fled Juba last week and went into hiding after new clashes broke out between his forces and government soldiers, saying he would only return when third party forces are deployed to act as a buffer.

Last week Kiir called on him to help bring peace or risked being removed.

Machar's Sudan People's Liberation Movement/Army in Opposition (SPLM/A-IO) Saturday nominated Gai, a decision Machar spokesperson blasted as an “illegal conspiracy” to oust Machar.

The move threatens to split the armed opposition into two factions: one backing Gai in Juba to support implementing peace implementation, and another faction that only recognizes Machar as the first vice-president according to the peace accord signed last August.

South Sudan gained independence from Sudan in 2011 following 50 years of Africa's long-running civil war. Two years later the country slid back into chaos after Kiir accused his longtime rival Machar of a coup which resulted in the death of tens of thousands of people and displaced 2.4 million others.

Last week fighting in Juba also forced 26,000 people to flee to neighboring Uganda, according to UNHCR spokesman Andreas Needham in Geneva.