JUBA, South Sudan

South Sudanese army announced Sunday the "defection" of a deputy commander in the military zone of the northeastern Upper Nile State, adding that he has joined a rebel group led by ex-Vice President Riek Machar.

"We have information indicating military coordination between [renegade deputy commander] Johnson Olony and the rebels in the attack that took place yesterday in Malakal city, the provincial capital of the Upper Nile state," army spokesman Philip Aguer said in a Sunday statement.

"Throughout last month, Olony continued to send misleading affirmations refuting his defection, but we were aware of his coordination with Machar through rebels present in Sudanese capital Khartoum," Aguer said.

On Saturday, South Sudanese Information Minister Michael Makuei accused Olony of fighting on the side of the "rebels," claiming that "Olony aided the rebels in crossing the river from the western side and in entering Malakal city."

James Gatdet, a spokesmen for the rebel Sudan People's Liberation Movement-in-Opposition, for his part, said that their forces "are in full control of Malakal city under the command of Gen. Johnson Olony, which he recaptured from the control of President Salva Kiir's forces".

"We're in control of the city and its surrounding areas," Gatdet said.

Last month, Malakal was the site of clashes between forces loyal to Olony and the guards of Upper Nile Governor Simon Kun Puoch following the death of the former's deputy at the hands of unknown assailants in the southeastern part of the city.

The government of South Sudan has since accused Olony of "defecting" – a claim which he continued to deny – and summoned him to Juba.

Last week, the government sent presidential guards troops as reinforcements to Malakal with the objective of disarming Olony after he refused to appear before the army's high military command in Juba.

A former rebel, Olony joined the South Sudanese government in 2012 after commanding a local militia that sought to retrieve territories belonging to al-Shalak tribe, which Olony claimed were seized by the Dinka tribe.

South Sudan is currently 16 months into a protracted political crisis following a power struggle within the ruling Sudan People's Liberation Movement.

In December of 2013, full-blown conflict erupted, which Kiir was quick to portray as a "coup attempt" by his sacked Vice President Machar.

The ensuing conflict has left tens of thousands of people dead, two million seeking refuge – both internally and as refugees in neighboring countries – and 2.5 million at risk of starvation in 2015, according to UN data.

On-again, off-again peace talks in Addis Ababa have failed to produce any tangible breakthroughs.