Juba (AFP) - Violence in South Sudan's civil war including the execution of scores of hospital patients is the worst seen for decades and is an "affront to human dignity", Doctors Without Borders said Tuesday.

"The conflict has at times seen horrific levels of violence, including against healthcare facilities," said Raphael Gorgeu, South Sudan chief for Doctors Without Borders (Medecins Sans Frontieres, MSF).

"Patients have been shot in their beds, and lifesaving medical facilities have been burned and effectively destroyed. These attacks have far-reaching consequences for hundreds of thousands of people who are cut off from medical services."

Thousands have been killed in the conflict in the world's youngest country, while more than 1.5 million have been forced to flee since the war broke out in mid-December. Peace talks are stalled.

"The violence carried out against the wounded and sick, and against those seeking shelter in hospitals and against medical facilities themselves, are not only violations of international laws and humanitarian principles, but an affront to human dignity," MSF said in a report that examined the situation over the last six months.

MSF, which has earned a reputation for working in some of toughest war zone conditions across the world, said the situation was the worst it had seen in years, even during the two decades long war that paved the way for South Sudan's independence from Sudan three years ago.

"Throughout its 30-year history in the country, MSF -- as well as other humanitarian organisations and healthcare providers -- has repeatedly witnessed violence against staff, patients, vehicles, compounds and healthcare facilities," MSF said, noting that at least 58 people were killed in the grounds of four hospitals.

"What has been particularly alarming in the current conflict, however, has been the scale and breadth of the violence."

Aid agencies warn of the risk of famine should fighting continue, and cholera is spreading, with over 50 people dead.

Fighting between forces of President Salva Kiir and troops loyal to rebel chief Riek Machar has been marked by widespread atrocities and, according to aid agencies, has pushed the world's youngest nation to the brink of famine.

Kiir and Machar committed themselves last month to a third ceasefire deal, and agreed to forge a transitional government within 60 days. Fighting continues.