South Sudan’s president has replaced his vice president and rival Riek Machar, in a move that could undermine last year’s peace accord and trigger a fresh wave of violence in Africa’s youngest nation.

The president said on Monday that he had replaced Machar with a former peace negotiator, General Taban Deng Gai.

Deng Gai, who had also been named leader of a faction of the armed opposition on Saturday, will serve until Machar returns to the capital, Juba, according to Machar’s chief of staff Ezekiel Lol Gatkuoth.

Machar, a former rebel leader, was sworn in as first vice president in April, eight months after the peace agreement was signed between the government and rebels loyal to him.

However, he left Juba with his troops earlier this month after fresh fighting erupted between his loyalists and government troops. Machar said he would only return if an international peacekeeping force guarantees his safety.

The last August peace deal put an end to two years of fighting that broke out when the president removed Machar as his deputy in 2013. The violence killed more than 10,000 people.

Clashes, however, erupted again between the two sides in Juba in early July, killing hundreds of people and forcing thousands of others to flee to neighboring Uganda, according to the United Nations refugee agency (UNHCR).

Forces from two rival groups fought each other with tanks, helicopters and other heavy weapons.

There are numerous militia forces that do not abide by peace agreements and are driven by local agendas.

The chaos comes as the country marked the fifth anniversary of its independence from Sudan earlier this month.