South Sudan’s military forces systematically raped women, murdered civilians and carried out large-scale looting, Amnesty International has alleged.

Civilians were burnt alive, hanged in trees and run over with armoured vehicles in opposition-held areas in Unity State, the group said, while children were swung into tree trunks to kill them.

The report is based on the testimonies of around 100 civilians who fled an offensive by government forces and allied youth militias in Mayendit and Leer counties between 21 April and early July this year.

Amnesty said it had called for an investigation after identifying four individuals it suspected of responsibility for war crimes and crimes against humanity following an offensive in Unity State in 2016.

But the South Sudanese authorities failed to respond to the warnings and recent UN reports suggest some of those identified by Amnesty may have also been involved in atrocities committed during the offensive this year.

Joan Nyanyuki, Amnesty International’s regional director for East Africa, said: “A key factor in this brutal offensive was the failure to bring to justice those responsible for previous waves of violence targeting civilians in the region.

“Leer and Mayendit counties have been hard hit in the past, and yet the South Sudanese government continues to give suspected perpetrators free rein to commit fresh atrocities. The result has been catastrophic for civilians.”

South Sudanese rebels Show all 25 1 /25 South Sudanese rebels South Sudanese rebels A rebel fighter near the town of Kaya on South Sudan’s border with Uganda a day before the 26 August assault Reuters/Goran Tomasevic South Sudanese rebels Thousands of rebel troops have been killed since civil war broke out in 2013 Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebels pray in Yondu, the day before an assault on government SPLA (Sudan People's Liberation Army) soldiers in the town of Kaya, on the border with Uganda, South Sudan, August 25, 2017 Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebels parade in Yondu, the day before an assault on government SPLA (Sudan People's Liberation Army) soldiers in the town of Kaya, on the border with Uganda, South Sudan, August 25, 2017 REUTERS/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebels parade in Yondu, the day before an assault on government SPLA (Sudan People's Liberation Army) soldiers in the town of Kaya, on the border with Uganda, South Sudan, August 25, 2017. REUTERS/Goran Tomasevic SEARCH "SPLA-IO" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES. Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebels stand in line during a parade in Yondu, the day before an assault on government SPLA (Sudan People's Liberation Army) soldiers in the town of Kaya, on the border with Uganda, South Sudan, August 25, 2017. Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebels stand in line during a parade in Yondu, the day before an assault on government SPLA (Sudan People's Liberation Army) soldiers in the town of Kaya, on the border with Uganda, South Sudan, August 25, 2017. REUTERS/Goran Tomasevic SEARCH "SPLA-IO" FOR THIS STORY. SEARCH Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebels stand in Yondu, the day before an assault on government SPLA (Sudan People's Liberation Army) soldiers in the town of Kaya, on the border with Uganda, South Sudan, August 25, 2017 Reuters/Goran Tomasevic South Sudanese rebels An elderly SPLA-IO (SPLA-In Opposition) rebel cries as he talks to other rebels in Yondu, the day before an assault on government SPLA (Sudan People's Liberation Army) soldiers in the town of Kaya, on the border with Uganda, South Sudan, August 25, 2017. REUTERS/Goran Tomasevic SEARCH "SPLA-IO" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES. TPX IMAGES OF THE DAY. Reuters/Goran Tomasevic South Sudanese rebels A SPLA-IO (SPLA-In Opposition) rebel carries a rucksack with picture of Bob Marley in Yondu, the day before an assault on government SPLA (Sudan People's Liberation Army) soldiers in the town of Kaya, on the border with Uganda, South Sudan, August 25, 2017 Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebels walk in Yondu, the day before an assault on government SPLA (Sudan People's Liberation Army) soldiers in the town of Kaya, on the border with Uganda, South Sudan, August 25, 2017 Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebels stand in Yondu, the day before an assault on government SPLA (Sudan People's Liberation Army) soldiers in the town of Kaya, on the border with Uganda, South Sudan, August 25, 2017 Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebels hold up guns in Yondu, the day before an assault on government SPLA (Sudan People's Liberation Army) soldiers in the town of Kaya, on the border with Uganda, South Sudan, August 25, 2017 Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebels march after an assault on government SPLA (Sudan People's Liberation Army) soldiers, near the town of Kaya, on the border with Uganda, South Sudan, August 26, 2017 Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebels walk during an assault on government SPLA (Sudan People's Liberation Army) soldiers in the town of Kaya, on the border with Uganda, South Sudan, August 26, 2017. Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebels walk during an assault on government SPLA (Sudan People's Liberation Army) soldiers in the town of Kaya, on the border with Uganda, South Sudan, August 26, 2017. Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebels return fire as they march after an assault on government SPLA (Sudan People's Liberation Army) soldiers in the town of Kaya, on the road between Kaya and Yundu, South Sudan, August 26, 2017. Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebel fires his rifle during an assault on government SPLA (Sudan People's Liberation Army) soldiers in the town of Kaya, on the border with Uganda, South Sudan, August 26, 2017 Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebel gestures during an assault on government SPLA (Sudan People's Liberation Army) soldiers in the town of Kaya, on the border with Uganda, South Sudan, August 26, 2017. Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebels fire weapons during an assault on government SPLA (Sudan People's Liberation Army) soldiers in the town of Kaya, on the border with Uganda, South Sudan, August 26, 2017. Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebels carry an injured rebel after an assault on government SPLA (Sudan People's Liberation Army) soldiers, on the road between Kaya and Yondu, South Sudan, August 26, 2017. Reuters/Goran Tomasevic South Sudanese rebels An injured SPLA-IO (SPLA-In Opposition) rebel lies on an improvised stretcher after an assault on government SPLA (Sudan People's Liberation Army) soldiers near the town of Kaya, on the road between Kaya and Yunde, South Sudan, August 26, 2017. Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebels stand after an assault on government SPLA (Sudan People's Liberation Army) soldiers, outside the town of Kaya, on the border with Uganda, South Sudan, August 26, 2017 Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebels march after an assault on government SPLA (Sudan People's Liberation Army) soldiers in the town of Kaya, on the road between Kaya and Yondu, South Sudan, August 26, 2017. Reuters/Goran Tomasevic South Sudanese rebels SPLA-IO (SPLA-In Opposition) rebels drink water from a pond after an assault on government SPLA (Sudan People's Liberation Army) soldiers near the town of Kaya, on the border with Uganda, South Sudan, August 26, 2017 Reuters/Goran Tomasevic

Unity State has been the site of the most ruthless violence since South Sudan’s civil war erupted five years ago.

At least 50,000 people have been killed during the conflict, many of them civilians, according to UN figures, and an estimated quarter of South Sudan’s population has been displaced.

Dozens of civilians told Amnesty about how, during the recent offensive, soldiers and militias used amphibious vehicles to hunt down civilians who had fled to nearby swamps.

Survivors described how groups of five or more soldiers often shot indiscriminately into the reeds as they searched for people.

One elderly woman, Nyalony, told Amnesty she saw her husband and two other men killed by soldiers: “When the attack started, early in the morning while we were sleeping, my husband and I ran to the swamp together. Later in the morning, after the fighting was over, the soldiers came into the swamp looking for people, and sprayed the area where we were hiding with bullets.

“My husband was hit; he cried out in pain. He was still alive, though, and the soldiers caught him, and then they shot him again and killed him. He was unarmed and wasn’t a fighter; just a farmer.”

Those who were unable to flee, especially the elderly, children and people with disabilities, were often killed in their villages.

Freed child soldiers with their rifles (CHARLES LOMODONG/AFP/Getty Images)

Several witnesses described how elderly relatives or neighbours were burnt alive in their tukuls (traditional dwellings) and one man in his 90s had his throat slit with a knife.

Nwaweke, 20, said she witnessed soldiers shooting her father and then murdering several children in the village of Thonyoor in Leer county: “There were seven men [soldiers] who collected the children and put them into a tukul and they set the tukul on fire.

“I could hear the screaming. They were four boys. One boy tried to come out and the soldiers closed the door on him.

“There were also five boys whom they hit against the tree, swinging them. They were two [or] three years old. They don’t want especially boys to live because they know they will grow up to become soldiers.”

An estimated quarter of South Sudan’s population has been displaced during the civil war (TONY KARUMBA/AFP/Getty Images)

Other survivors described similar horrors, including one in Rukway village in Leer where an elderly man and woman were burnt to death in a house along with their two young grandsons.

When their daughter ran out with a small baby, a soldier shot her and crushed the baby to death with his foot.

Amnesty’s report also detailed how government and allied forces abducted primarily women and girls and held them for up to several weeks, with many women and girls gang-raped. Those who attempted to resist were killed.

One interviewee said a girl as young as eight was gang-raped and another woman saw a 15-year-old boy being raped.

A 60-year-old man described finding his 13-year-old niece after she was gang-raped by five men: “My brother’s daughter was raped and she was going to die.

“When they raped her, we came and found her and she was crying and bleeding … she couldn’t hide … she told me she was raped by five men. We could not carry her and she could not walk.”

Amnesty has called on South Sudan’s government to end all atrocities and immediately establish the Hybrid Court of South Sudan, which has been in Limbo since 2015.