ADDIS ABABA (Reuters) - South Sudanese rebels accused the government army of attacking one of their bases overnight as a new round of peace talks between the warring sides opened in the Ethiopian capital on Monday.

Rebel spokesman Lam Paul Gabriel said government troops attacked a rebel base in the town of Lasu in the south of the country late on Sunday.

“They are in the IO base,” he said, referring to the name of the rebel group. Army spokesmen were not immediately available to comment when called by Reuters on Monday afternoon.

The talks in Addis Ababa have been convened by the East African bloc IGAD and are aimed at bringing the warring sides back to the negotiating table after a 2015 peace deal collapsed last year during heavy fighting in the capital, Juba.

The war began in 2013 between soldiers of President Salva Kiir, an ethnic Dinka, and his former vice president, Riek Machar, a Nuer. Tens of thousands of people have died and a third of South Sudan’s 12 million population have fled their homes.

Highlighting the widespread nature of the violence, army spokesman Lul Ruai Koang earlier said four aid workers from the French organization Solidarites International had been kidnapped a day earlier by the rebels near the western city of Raja.

The state government, based in Raja, said in a statement eight civilians had been killed and the four aid workers kidnapped in what it described as an ambush by the rebels.

The French organization said it had lost contact with three members of its team on Saturday. It gave no indication of their fate and it was not immediately clear why it gave a different number of those involved.

An IO rebel statement said: “The SPLA IO forces also rescued four humanitarian staff ... they are currently safe and sound with our forces around Raja and will be handed over ... as soon as possible.”

It was not immediately clear what the rebels said they had rescued the aid workers from.

The war has mutated from a two-way fight into a fragmented conflict, making peace more elusive, the top United Nations peacekeeper in the country told Reuters earlier this year.

Diplomats and analysts question whether the will to end the fighting exists, as Kiir’s government holds the military upper hand and rebel leader Machar is under house arrest in South Africa. [L3N1NG5D4] Machar sent representatives to the Ethiopian capital for the talks.

Ethiopian Prime Minister Hailemariam Desalegn voiced strong criticism of the warring sides at the forum in Addis Ababa.

“... More than half of the people of South Sudan are either refugees in neighboring countries, internally displaced within South Sudan or suffering from food insecurity in their own village,” he said.

“It is equally clear that all this suffering is taking place because you the leaders of South Sudan have repeatedly failed to talk to each other, to negotiate, to be tolerant, to make compromises,” he added. “Today, I appeal to you to stop this intransigence.”