Martha Nyarueni (R) and her family return to their home outside of the town of Leer, South Sudan, after receiving aid package, on July 5, 2014
Addis Ababa (AFP) - Peace talks to end South Sudan's civil war resumed Monday, but fighting continued with gunmen shooting dead an aid worker amid warnings of looming famine.
As delegates gathered for talks in Ethiopia, rampaging militia forces in South Sudan's Upper Nile state battled deserting soldiers for a second day, with aid workers sheltering in UN compounds mourning a colleague who was murdered.
The UN peacekeeping mission in South Sudan (UNMISS) said it was "deeply concerned about the deteriorating security situation" in Bunj in the northeastern state of Upper Nile, where aid workers are supporting more than 125,000 refugees from neighbouring Sudan.
On Monday, "members of the militia shot and killed a staff member" of an aid agency, after gunmen demanded to know the ethnicity of staff members, UNMISS said.
The aid worker was reported to have been South Sudanese.
"UNMISS strongly condemns the targeted killing of civilians by members of this militia," it said in a statement, calling for calm "before the situation descends into lawlessness".
In Ethiopia, mediators on Monday warned that rival leaders would face repercussions if fighting continued.
The regional bloc brokering the talks, IGAD, has set an August 10 deadline for both sides to agree on a transitional government and implement a ceasefire.
The last round of peace talks between President Salva Kiir and his former deputy Riek Machar stalled in June with each side blaming the other for the failure.
"This session of negotiations must make progress, we must end the war," chief mediator Seyoum Mesfin said at the opening of talks in the Ethiopian capital.
If war continues "it will have serious consequences... those that insist on continued fighting must be held accountable," he added.
- 'Bloodshed and suffering' -
The United States and the European Union have slapped sanctions on senior military leaders on both sides, and IGAD leaders have threatened measures if both sides continue to violate previous peace deals.
Thousands of people have been killed and over 1.5 million have fled more than seven months of fighting between government troops, mutinous soldiers and ragtag militia forces divided by tribe.
Aid agencies have warned of the likelihood of famine within weeks if fighting continues.
China's ambassador to Ethiopia and the African Union criticised talks for moving at a "snail's pace" and said the world was losing patience.
"The patience of the regional countries and the international community are being worn out because they haven't seen real results, they see only the looming famine and the continued suffering of the people there," said Ambassador Xie Xiaoyan.
China, which has major investments in South Sudan's oil fields, has closely followed the talks since they started in January.
On Monday, the government blamed rebel chief Machar of launching fresh attacks.
"Riek Machar... should not waste any more time over military campaigns," said the head of the government delegation, Nhial Deng Nhial.
Previous rounds of talks, held in luxury hotels in Addis Ababa, have already cost at least $17 million (12 million euros) but have yielded few results.
Aid agency Oxfam called on the delegates to "end the bloodshed and suffering."
"As South Sudan sits on the brink of famine, the international community needs to do everything it can to support this young nation to urgently scale up the humanitarian response to save lives," said Oxfam South Sudan country director Tariq Riebl.