By Agencies

Witnesses say soldiers and militiamen targeted civilians by raping them, burning them alive, and killing male infants.

South Sudan's government and its allied militias have been accused of carrying out war crimes of "staggering brutality" during an offensive earlier this year.

Witnesses described how soldiers and fighters targeted civilians by raping them, burning them alive, running them over with armoured vehicles, and hanging them from trees, Amnesty International said in a report on Wednesday.

"One interviewee said a girl as young as eight was gang-raped and another woman witnessed the rape of a 15-year-old boy," it said.

The report was based on interviews with 100 displaced people from Leer and Mayendit counties in Unity State, which have been among the hardest hit regions during South Sudan's five-year civil war.

Amnesty also documented the abduction of women and girls, and the deliberate killing of young boys and male infants. The attacks continued for a week after a ceasefire was announced.

"The government attacked dozens of civilians in these areas, burning houses systematically, killing people - including women, children, and elderly people," Amnesty's Joanne Mariner said.

"We documented horrific cases in which elderly people - 70, 80, even 90 years old - were burned alive inside houses because the government was torching villages in a really systematic way."

The killings echo the type of brutality meted out to civilians that have characterised South Sudan's war since its start.

South Sudan's government often dismisses such reports as "rubbish".

Africa's refugee crisis 

President Salva Kiir and rebel leader Riek Machar signed a new peace deal in Ethiopia last week after lengthy negotiations.

It allows the creation of a transitional government, with Machar to be reinstated as vice president.

Despite the breakthrough, many international observers remain sceptical as previous agreements have collapsed after warring parties failed to respect them.

Years of conflict in South Sudan has left more than half of its 12 million populations in need of food aid for survival.

The world's newest country descended into civil war in 2013 after Kiir accused Machar, then his deputy, of plotting a coup.

The conflict has killed tens of thousands of people with more than two million fleeing the country, creating Africa's largest refugee crisis since the 1994 Rwandan genocide.