Delegates from South Sudan's warring factions are expected to meet for talks in the Ethiopian capital on Sunday.
Face-to-face peace talks between South Sudan's warring factions are set to begin in earnest on Sunday, with artillery fire in Juba's government district underlining the risk of a slide into all-out civil war.
The talks in the Ethiopian capital are aimed at ending three weeks of fighting that are feared to have killed thousands in the world's newest nation.
"South Sudan deserves peace and development not war," Ethiopian Foreign Minister Tedros Adhanom said at ceremony to formally open talks on Saturday, which bring the government and rebel teams together for the first time.
"You should not allow this senseless war to continue, you need to stop it, and you need to stop it today—and you can."
As delegates smiled in a luxury hotel in Ethiopia, heavy explosions from artillery fire and the rattle of automatic weapons were heard in a Juba district where most ministries, the presidential palace and the Parliament are located, an Agence France-Presse reporter said.
It was not clear who was involved in the fighting, that ended a period of relative calm in the capital.
The conflict erupted on December 15, pitting army units loyal to President Salva Kiir against a loose alliance of ethnic militia forces and mutinous army commanders nominally headed by his rival, former vice-president Riek Machar.
A spokesperson for the EU's foreign policy chief Catherine Ashton welcomed the opening of the peace talks, while calling for the release of all detained political leaders.
"We call on both parties to desist from public statements that might incite their followers," the spokesperson added.
Negotiation teams have already spent three days in neighbouring Ethiopia's capital Addis Ababa.
Ethiopian foreign ministry spokesperson Dina Mufti said the full formal direct talks would begin at noon GMT on Sunday.
"The people of South Sudan have suffered in the fight for independence, and they will not suffer again in our hands," said Nhial Deng Nhial, head of the government negotiation team.
"We shall leave no stone unturned in the search for a peaceful resolution."
But Nhial also warned it "must be abundantly clear" the government has "an obligation to restore peace and security of the country through all means available".
Fighting has spread across the world's youngest nation, with the rebels seizing several areas in the oil-rich north.
Rebel delegation chief Taban Deng, a former governor of the key oil-state Unity, said they were committed to the talks mediated by the regional East African IGAD bloc of nations.
"We will be continuing [to] move to the next level," Deng said, including negotiating ceasefire and "political issues".
Deng demanded the release of several top political leaders from the ruling Sudan People's Liberation Movement (SPLM), accused of involvement in the violence, that began in an alleged coup attempt.
Aid workers have stepped up warnings of a worsening crisis for civilians affected by the conflict in the landlocked country of almost 11-million.
Battle for Bor
The army continued on Saturday to battle rebels in a bid to wrest back the strategic town of Bor, capital of Jonglei, one of the country's largest states.
"Our forces are still moving towards Bor," army spokesperson Philip Aguer told AFP, dismissing rebel claims they had been marching on Juba.
There were reports of intense battles involving tanks and artillery on the outskirts of Bor, which has already exchanged hands three times since fighting began.
The US embassy in South Sudan ordered a further pull-out of staff on Friday because of the "deteriorating security situation", although Washington—a key backer of the fledgling state—insisted it remains committed to ending the violence.
The ongoing fighting prompted the top UN aid official in South Sudan, Toby Lanzer, to warn that soldiers and rebels must protect civilians and aid workers.
He announced on Saturday that the UN peacekeeping force (UNMISS) would be "reinforcing its presence" in the country.
IGAD, the Inter-Governmental Authority on Development, whose members include Ethiopia as well as Kenya and Uganda—all strong backers of Kiir's government—played key roles in pushing forward the 2005 deal that ended Sudan's two-decade-long civil war.
"If you put your people and country above any personal ambitions, surely you can stop the war," Ethiopian Foreign Minister Tedros said.
Fighting started in oil-rich but impoverished South Sudan when Kiir accused Machar of attempting a coup.
Machar denied this, in turn accusing the president of conducting a violent purge of opponents.
The violence has forced around 200 000 people to flee their homes and "affected many hundreds of thousands of people indirectly", the UN's Lanzer said. Tens of thousand are seeking refuge with badly overstretched UN peacekeepers.
The UN peacekeeping force said this week that atrocities are continuing to occur throughout South Sudan, which won independence from Sudan in 2011 after decades of civil war.
The conflict has been marked by an upsurge of ethnic violence pitting members of the Dinka tribe that Kiir comes from against the Nuer people of Machar. - AFP