Women and children are increasingly targeted in a surge of violence in South Sudan's Jonglei state, riven by ethnic killings, a rebellion and an army crackdown, Doctors Without Borders said Tuesday.

"Tens of thousands of men, women and children have been repeatedly attacked, killed and displaced, with devastating impacts on their lives," the report by the medical aid agency MSF read, documenting an upsurge in violence since 2011.

"The lives and health of Jonglei's population are hanging by a thread," said Chris Lockyear, MSF's operational manager, warning of a further "spike in violence" in the approaching dry season.

Violence includes an escalation of traditional cattle raiding between rival tribes into a wave of brutal revenge attacks, exacerbated by an easy availability of automatic weapons.

The nature of the attacks is shifting, MSF said, documenting multiple cases of rape in the vast and grossly impoverished state, while four of MSF's six clinics in Jonglei have also been looted or destroyed since 2011.

"While appropriating cattle used to be the main aim of the attacks, nowadays civilians are targeted, with women and children making up a large proportion of victims treated by MSF teams," the report read.

More than 2,600 people have been killed in Jonglei in the past 18 months, according to the United Nations.

"They set huts on fire and threw children in the fire," said one 55-year-old woman treated by MSF, whose testimony of an attack by unidentified gunmen is quoted in the report.

"Because I am old, I cannot run fast and they killed the children that were with me," she said. "If the child can run, they will shoot them with the gun; if they are small and cannot run, they will kill them with a knife."