Rebels fighting against the South Sudanese government say that 700 men from government troops have defected with all their equipment and joined them.

South Sudanese President Salva "Kiir's army has suffered its biggest yet mass defection since the current conflict began on 15th December," rebel spokesman Lul Ruai Koang said in a statement issued on Thursday.

Koang said the defectors "engineered an internal revolt, opened fire on loyalist soldiers and in the process killed the commanding officer with the rank of colonel."

The men then "joined the rebellion with their equipment," which included 16 trucks, some of them mounted with machineguns, the statement said.

The fighting between troops of Kiir, who is from the Dinka ethnic group, and his former deputy, Riek Machar, a Nuer, erupted around Juba on December 15, 2013.

The conflict soon turned into an all-out war between the army and defectors, with the violence taking on an ethnic dimension that pitted the president’s tribe against Machar's.

The International Crisis Group said on January 9 that about 10,000 people had been killed in the violence.

South Sudan gained independence in July 2011 after its people overwhelmingly voted in a referendum for a split from the North.

The government in Juba is grappling with rampant corruption, unrest and conflict in the deeply impoverished but oil-rich nation, left devastated by decades of war.