Weeks after UN-backed experts warned that thousands are dying of starvation in South Sudan war zones, aid agencies say they cannot access areas to stave off famine because of "spiraling" violence.

Weeks after UN-backed experts warned that thousands are dying of starvation in South Sudan war zones, aid agencies say they cannot access areas to stave off famine because of "spiraling" violence.

Last month, UN agencies said 30,000 people were starving to death in Unity state, with Integrated Food Security Phase Classification (IPC) experts warning of a "concrete risk of famine" before the end of the year if fighting continues and aid does not reach the hardest hit areas.

Despite the warnings and an August peace deal, there has been no let-up in government and rebel battles, with diplomats accusing both sides of blockading life-saving aid.

Medical aid agency Doctors Without Borders (MSF) warns that the "humanitarian crisis in southern Unity is on an unprecedented scale" with "repeated and targeted violence" against civilians.

MSF, which has earned a reputation for operating in some of the world's most dangerous frontline battle zones, said it had "not seen this level of violence and brutality before."

While an official famine has not been declared, the IPC report describes the worst conditions yet seen in a nearly two-year civil war marked by atrocities and accusations of war crimes, including gang rape and forced cannibalism.

Having been forced to flee their homes, many people are living in the open, said Lindsay Hamsik, policy advisor at South Sudan NGO Forum, an alliance of over 300 South Sudanese and international aid agencies.

"The commitments at the political level are not being held up on the ground," Hamsik told AFP. "That means more lives are being lost and civilians continue to be terrorized and denied their right to assistance."