Warfare in the world's newest state has displaced more than 400,000 people since mid-December, with the front lines constantly shifting as loyalist troops and renegade forces gain and lose territory in battles often waged along ethnic lines.
Lt. Col. Philip Aguer, the South Sudanese military spokesman, said there was fighting about 70 kilometers (45 miles) north of the South Sudanese capital of Juba. Heavy fighting also erupted Tuesday in Malakal, the capital of oil-producing Upper Nile state, which renegade forces briefly held before government troops retook it, he said.
As control of certain regions has changed, tens of thousands of residents have fled their homes to escape fighting that often pits the Dinka ethnic group of President Salva Kiir against the Nuer group of Riek Machar, the former vice president who now commands renegade forces. A boat on the Nile - fleeing the violence in Upper Nile State and carrying mostly women and children- sank on Saturday, killing at least 200 people, according to Aguer.
The violence has displaced 413,000 people, including more than 73,000 who sought refuge in neighboring countries, according to the United Nations. Some of the fiercest battles have been fought in Jonglei, South Sudan's largest state, where for months government troops had been trying to put down a local rebellion. South Sudan's government now says it has made peace with the leader of that rebellion, David Yau Yau, a renegade colonel from the Murle tribe who appears to have cut a deal with the Dinka-led government against Machar's mostly Nuer forces.
South Sudan has a history of ethnic rivalry, and its many tribes have long battled each other in recurring cycles of violence.
Nearly 10,000 people have been killed in the latest fighting, according to one estimate by an International Crisis Group analyst.
The Associated Press has seen video showing a representative of Kiir's government meeting with Yau Yau in Jonglei's Pibor county earlier this week after the militia leader agreed to integrate his fighters into the national army. In the video bodies of men in combat fatigues litter the bushes, but it is impossible to tell if the dead are rebels or government troops.
Troops from neighboring Uganda appear to be actively fighting on behalf of Kiir, who is reportedly seeking the long-term commitment of Ugandan troops in the fight against renegade forces.
In Ethiopia, where peace talks are taking place, a spokesman for the rebels, former South Sudan Brig. Gen. Lul Ruai Kong, said Ugandan helicopters and fighter jets are bombing rebel positions.
Another pro-rebel official, Gideon Gatpan Thaor, said fighters described being hit with a smoky weapon that burns, possibly white phosphorous.
A Ugandan military official denied Ugandan forces are already involved in active combat but admitted that is where they are headed following the rebels' threat to take Juba, where fighting erupted on Dec. 15 before it spread across the oil-producing East African country.
Lt. Col. Paddy Ankunda, the Ugandan military spokesman, said Tuesday that Ugandan and South Sudanese army officials are drafting a "status of forces agreement" that will soon be signed by both countries after Kiir requested the Ugandans extend their deployment.
When that pact is signed, he said, "there could be things under the agreement which the forces might engage in." He said a Ugandan army colonel previously with the African Union peacekeeping force in Somalia has been appointed as head of Ugandan forces in South Sudan, part of wider efforts by Uganda to formalize a mission that is increasingly controversial at home and abroad.
On a recent trip to Juba, Ugandan President Yoweri Museveni warned Machar that East African countries would unite to "defeat" him if he did not start talks with the government.
It now appears Museveni is going it alone, sending to South Sudan thousands of men and hardware that may have given government forces an edge against rebels who threatened Juba. Kiir has refused to release the political detainees who are Machar's allies, one of the conditions set by the rebels before they can sign any cease-fire deal with the government.
Ugandan officials initially said troops were deployed to South Sudan to protect key installations such as the airport as well as to facilitate civilian evacuations.
Amid rumors some Ugandan forces have been killed or wounded in South Sudan, Ugandan lawmakers on Tuesday met for a special session to discuss the legality of the deployment.
Museveni is highly influential in Juba, where his prestige is based in part on his decades-long support for the armed secessionist movement that eventually led to the creation in 2011 of the new state of South Sudan.
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