South Sudan's President Salva Kiir met Thursday with rebel leader Riek Machar for the latest round of peace talks aimed at resolving the fledgling nation's 13-month-old civil war.

The negotiations, which are taking place in the Ethiopian capital of Addis Ababa, are being facilitated by mediators from the Intergovernmental Authority on Development in Eastern Africa (IGAD).

Dismissing reports that Kiir had fallen ill during the negotiations, his spokesman Ateny Wek said the president "is doing his duties to restore peace." The meeting between the two leaders, "was aimed at narrowing the gap in the negotiations in an attempt to arrive at finding a peaceful solution," Ateny said.

When asked if there had been progress made in the talks, Machar told AFP news agency, "not yet."

The two leaders will hold additional talks with regional leaders after the opening of an African Union summit in the Ethiopian capital on Friday and Saturday.

Kiir and Machar met earlier this month in Tanzania to sign a ceasefire - since broken - and promised to "make a public apology for what has happened" since the war broke out.

'The largest mass grave'

Meanwhile, rebel military spokesman Lul Ruai Koang said on Thursday that government forces were advancing in Jonglei state in the country's east, warning that rebel forces would create "the largest mass grave" for attacking troops.

"Any attempt…at invading our areas will meet strong resistance," Koang said.

South Sudan, the world's youngest nation, has been mired in a civil war since 2013 when Kiir accused his then-deputy Machar of attempting a coup. Since then, fighting has continued along ethnic lines between the ethnic Dinka supporting Kiir and the Nuer supporting Machar.

Since the fighting broke out, tens of thousands have been killed in a war marked by massacres, gang-rape, and child soldier recruitment. A ceasefire between the warring factions has been broken six times and the nation has been driven to the verge of famine.

Rebels recently agreed to release about 3,000 child soldiers, but thousands more are still fighting. According to UNICEF, nearly 12,000 children have been forcibly recruited by armed groups across South Sudan.

More than two dozen armed groups are involved in the fighting, including various militia groups, rebels from the Darfur region of neighboring Sudan, as well as Ugandan troops supporting Kiir.

bw/msh (AFP, dpa)