Thirteen South Sudanese soldiers accused of raping five foreign aid workers and killing John Gatluak, their local colleague, appeared before a military court on Tuesday, a case seen as a test of the government's ability to put people on trial for war crimes.

The attack, one of the worst on aid workers in South Sudan's civil war, took place on July 11, 2016, as President Salva Kiir's troops won a three-day battle in Juba over opposition forces loyal to former Vice President Riek Machar.

Describing the incident, the manager of the Terrain Hotel where the attack happened, Mike Woodward, told the court that "between 50 to 100" soldiers arrived in the hotel in the afternoon of July 11 and began looting an hour later.

"Five women working with humanitarian organisations were then raped. John Gatluak was shot at 6:15pm," Woodward said.

Peter Malual, the defendants' lawyer, dismissed the charges, saying evidence provided by Woodward was not sufficient to prove the allegations.

"What I know the area was under operation at the time and rebels were controlling the area," Malual said.

Prosecutors told Reuters the alleged murderers face a minimum of 10 years in jail with a fine paid to the victim's family, or a maximum of the death penalty. Those accused of rape face up to 14 years. Court officials said the trial would resume on June 6.

Witnesses told Reuters news agency at the time that armed men attacked the hotel in the capital, Juba, for several hours. Victims phoned UN peacekeepers stationed a mile away and begged for help, but none came, the witnesses said.

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The military head of the UN peacekeeping mission was fired and the political head resigned over the incident.

UN investigators and rights group have frequently accused both the army and rebels of murder, torture and rape since the civil war began in 2013, and say the crimes almost always go unpunished.

The three-year conflict has fractured the country along ethnic lines - Kiir is an ethnic Dinka, Machar is a Nuer - and forced a quarter of the country's 12 million population to flee their homes.