Peace talks between South Sudan's government and rebels aimed at ending a four-month-old civil war resumed in the Ethiopian capital on Monday, amid mounting global outrage over a wave of atrocities.

The long-awaited resumption of the talks, which have been on hold for several weeks against a backdrop of heavy fighting, came as top U.N. human rights officials arrived in the country to probe massacres and other war crimes.

When not plotting military strategy to seize South Sudan's crucial oil fields, sacked vice-president turned rebel chief Riek Machar spends time reading the economic and political history "Why Nations Fail".

Cynics might argue he would do better to simply look around his basic bush camp, where mutinous soldiers and an allied ethnic militia crammed with child soldiers ready themselves to attack government forces, as a brutal four-month-long civil war in which thousands of people have already been killed intensifies.

Like many 13 year-olds, Gach Chuol is timid, shyly looking down at the ground as he speaks to a stranger.

But he is also joining South Sudan's war to avenge the death of his parents, and brandishes an AK-47 assault rifle as he recalls why he traded his school books for arms.

Gunmen opened fire on a truck in western Ethiopia Wednesday, killing nine people and injuring seven, the information ministry said.

"Unidentified armed men opened fire on a truck carrying 28 people, killing nine on board," it said in a statement.

Ethiopia is using foreign technology to spy on citizens suspected of being critical of the government, Human Rights Watch said in a report released Tuesday.

The report accused the government of using Chinese and European technology to survey phone calls and Internet activity in Ethiopia and among the diaspora living overseas, and HRW said firms colluding with the government could be guilty of abuses.

Somali government forces backed by African Union troops captured a sixth settlement in the latest advance in their renewed offensive against al-Qaida-linked Shebab fighters, a spokesman said Friday.

Shebab gunmen are reported to have fled ahead of the assault on Thursday on the small town of Buula Burde, in the southern Hiran region bordering Ethiopia, Ali Houmed said, spokesman of the African Union's AMISOM force.

East African heads of state met in Addis Ababa Thursday in the latest push for peace in war-torn South Sudan, where almost three months of raging conflict has left thousands dead.

Leaders from the East African bloc, the Intergovernmental Authority on Development (IGAD), were hosted by Ethiopian Prime Minister Hailemariam Desalegn to "deliberate on the current situation" in the troubled fledgling nation, a statement read.

African peacekeepers in Somalia operating with government forces have recaptured several strategic towns in the southwest from the al-Qaida-linked Shebab militia, officials said Sunday.

The African Union's AMISOM force announced it had launched a widescale offensive on Thursday against the Islamist fighters in areas near the Ethiopian border.

The World Food Program said Friday it was planning to airlift and airdrop urgently needed food aid to thousands of refugees and others affected by the conflict in South Sudan.

The UN agency said the conflict in the world's newest nation had severely complicated supplying refugee camps in the northeastern Maban County with food, warning that cereal stocks there were exhausted.

War crimes have been committed by all sides in conflict-wracked South Sudan, Human Rights Watch said Thursday, reporting widespread atrocities in weeks of carnage in the world's youngest nation.

Thousands have been killed and almost 900,000 forced from their homes by over two months of battles between rebel and government forces, backed by troops from neighboring Uganda.