Juba (AFP) - Rebels in South Sudan rejected UN reports they had massacred hundreds of civilians as "lies" Tuesday, as they wrested another town from government troops in a worsening civil war.
The rebels seized the town of Bentiu last week, unleashing two days of ethnic slaughter as they hunted down civilians sheltering in mosques, churches and a hospital, butchering dozens on the roadside, according to the United Nations.
But rebel spokesman Lul Ruai Koang praised the "gallant forces" of the insurgents, who the UN said took to the radio to urge men to rape women from the opposition ethnic group and drive out rivals from the town.
"The government forces and their allies committed these heinous crimes while retreating," Koang said, adding that the rebel offensive targeting oil fields was continuing.
However, the UN said the killings continued for almost two days after the rebels issued a statement boasting of victory in Bentiu, a time when Koang previously said gunmen were "mopping and cleaning up" in the town.
Bentiu is the capital of the key oil-producing state of Unity.
Government forces said they have been forced to pull out of another major settlement nearby amid furious rebel attacks.
South Sudan's army has been fighting rebels loyal to sacked vice president Riek Machar since the unrest broke out more than four months ago.
The conflict has taken on an ethnic dimension, pitting President Salva Kiir's Dinka tribe against militia forces from Machar's Nuer people.
- 'Piles of bodies' -
"The battles have been very heavy in Unity state," army spokesman Philip Aguer told AFP, adding that troops made a "tactical withdrawal" from the town of Mayom, a strategic local centre made up of dusty roads and thatch huts, some 50 kilometres (30 miles) west of Bentiu.
"Fighting is ongoing, we are close by and will not let the rebels advance further," Aguer said, insisting that the army remained in control of major oil fields and the country's refinery, also in Unity state.
The scale of killings in Bentiu is one of the worst atrocities in the four-month conflict.
Toby Lanzer, the top UN aid official in the country, told AFP after visiting Bentiu he had witnessed the "most terrible sight".
"There are piles of bodies lining the streets where they had been executed, in the market, outside and inside places of worship... the majority wearing civilian clothes," Lanzer said Monday.
The United States has threatened sanctions against those responsible for continuing the war.
The US ambassador to the UN Samantha Power said Tuesday that "all responsible for South Sudan horrors and deliberately targeting civilians must be held accountable."
- 'Unspeakable violence' -
Heavy fighting on Tuesday was also reported in the eastern state of Jonglei, and in Upper Nile in the northeast, with Aguer boasting the army had repulsed the attacks and killed scores of rebels.
"In Upper Nile... the number of rebels killed was 48," he said. The claims were not possible to independently verify.
In Bentiu, some 23,000 terrified civilians have crowded into the cramped UN peacekeeping base for protection, where under both fierce heat and heavy rains -- and little if any shelter -- they are surviving on just a litre (quart) of water a day each.
Jonathan Veitch, the UN children's agency chief in the country, warned of fatal water-borne diseases, saying that "children have endured unspeakable violence."
The UN has said more than one million people are at risk of famine.
On Tuesday, 22 international aid agencies, including Oxfam, Care and the International Rescue Committee, issued a joint warning they were already witnessing "alarming rates of malnutrition".
The conflict in South Sudan, which only won independence from Sudan in 2011 and is the world's youngest nation, has left thousands of people dead and forced around a million to flee their homes.
The fighting has been marked by reports and allegations of atrocities by both sides.
Peace talks are due to restart in neighbouring Ethiopia later this month, and despite the worsening conflict, South Sudan Information Minister Michael Makuei said the government remained committed.
"What we want is peace not war.... We will still go and negotiate," he told AFP, but said he feared rebels wanted to fight on, and that if so, the government had the "duty to protect its citizens".