Warring fighters in South Sudan have looted hospitals and murdered patients in their beds, cutting life-saving healthcare to hundreds of thousands of people, Doctors Without Borders said Wednesday.

Warning of an "alarming pattern of looting and attacks on patients" and health facilities, Doctors without Borders (MSF, Medecins sans Frontieres) said their crucial work was being strangled by a "climate of utter disrespect and fear."

Key peace talks between South Sudan's government and rebels got under way in Ethiopia on Wednesday with regional mediators shuttling between delegates from both sides, a statement said.

The talks are aimed at building on a fragile ceasefire agreement that was signed in Addis Ababa on January 23 and addressing the root causes of the nearly two-month-old conflict in the world's youngest nation, which won independence from Khartoum just two and a half years ago.

Regional mediators formally opened a new round of South Sudan peace talks Tuesday with an opening ceremony held in the Ethiopian capital Addis Ababa, an Agence France Presse correspondent said.

The talks, involving representatives of President Salva Kiir and rebel leader Riek Machar, are set to begin in earnest on Wednesday morning and are aimed at addressing the root causes of the nearly two-month-old conflict in the world's youngest nation.

A new round of peace talks between South Sudan's government and rebels aimed at ending a nearly two-month-old conflict in the world's youngest nation has been postponed, officials said Monday.

The talks, which were due to open in Ethiopia, are aimed at building on a shaky ceasefire agreement and bringing about a comprehensive and durable solution by addressing the root causes of the conflict.

The United Nations issued an urgent appeal Tuesday for 1.27 billion dollars for aid for South Sudan, hit by a seven-week-old conflict that has forced close to a million people from their homes.

"The priority is to save lives now, and ensure that we have food, medicine and other lifesaving supplies pre-positioned in the field, in easy reach of aid agencies before the rains hit and the roads become impassable," said Toby Lanzer, the U.N.'s top aid official in South Sudan.

Conflict in the Central African Republic and South Sudan dominated the agenda as Africa's leaders met in Ethiopia Thursday for a two-day summit.

The African Union meeting, opened by outgoing chairman and Ethiopian Prime Minister Hailemariam Desalegn, is officially focused on agriculture and food security.

Mauritanian President Mohamed Ould Abdel Aziz took over as African Union chairman on Thursday, replacing Ethiopian Prime Minister Hailemariam Desalegn in the one-year post.

Aziz, in his opening speech, congratulated Hailemairan "for the remarkable work accomplished during his tenure," adding that "he has contributed brilliantly to strengthen the role of Africa on both continental and international levels".

Somalia's Shebab insurgents called Saturday for renewed attacks against foreign forces, after arch-enemy Ethiopia joined the African Union force battling the extremists.

Top commanders of the al-Qaida-linked group, including insurgent supremo Ahmed Abdi Godane, met this week after Ethiopia formally joined the U.N.-backed mission known as AMISOM, Shebab spokesman Ali Mohamud Rage told Agence France Presse.

East African nations have approved a 5,500-strong military force for war-torn South Sudan to end weeks of bitter fighting that has devastated the young nation, Kenya's foreign minister said Wednesday.

Thousands have been killed and half a million civilians forced to flee the fighting between troops loyal to President Salva Kiir and rebels allied to his sacked deputy Riek Machar.

Ethiopian troops in Somalia on Wednesday formally joined the U.N.-backed African Union force amid efforts to boost operations against Al-Qaeda-linked Shebab rebels, officials said.

Hardline Shebab insurgents control large parts of rural southern Somalia, having been driven from a string of towns by the African Union mission in Somalia (AMISOM), although guerrilla units stage regular deadly attacks in the capital Mogadishu.