In what is likely the worst single mass fatality incident since the outbreak of fighting in South Sudan last month, as many as 300 people drowned when an overloaded ferry that they had boarded to flee renewed clashes sank Tuesday in the White Nile. Many of the victims were women and children.

The victims had been attempting to escape Malakal, the capital of Upper Nile, an oil-rich state in the country’s northeast on the border with Sudan. Control of the area has been in continuous flux since the political conflict between President Salva Kiir and ousted Vice President Riek Machar erupted into armed conflict on December 15.

The mass drowning came amid growing indications of a humanitarian catastrophe unleashed by the month of fighting, which has seen ethnic-based massacres carried out both by forces loyal to the government of Kiir, from the Dinka tribe, the country’s largest ethnic group, and those backing Machar, who is from the Nuer, its second largest.

According to UN figures, nearly half a million people have been forced from their homes by the fighting, with 413,000 internally displaced and at least 75,000 having fled to neighboring countries.

While the UN last put the number of fatalities at “substantially more than 1,000 dead,” the International Crisis Group estimated last week that the figure had grown to nearly 10,000. The UN has reported atrocities on both sides.

The conflict has its roots in a bitter power struggle within the ruling SPLM (Sudanese People’s Liberation Movement) that has been developing since President Kiir sacked Machar as vice president, dismissed his entire cabinet and suspended the secretary-general of the SPLM, Pagan Amun, who was placed under investigation for allegedly inciting unrest. Machar made it known that he intended to challenge Kiir for the party leadership and run for president in the 2015 election. Machar also drew support from a number of senior military officers who were summarily dismissed.

The moves represented a consolidation of near-dictatorial powers and were accompanied by a turn toward stepped-up state repression. In removing Machar and all other Nuer representatives from the government, Kiir also set the stage for the political power struggle to become enmeshed in ethnic-based violence.

The fissures within the ruling party go back a long ways to the protracted civil war in the Sudan that culminated in the South Sudan’s separation as an independent state, which took place three years ago with strong US backing.

Machar had split from the SPLM in the 1990s, advocating an independent South Sudan, while at the time the SPLM backed a secular and democratic united Sudan, with full rights for southerners. The result was a civil war within the South Sudanese factions, including ethnic-based bloodletting, most infamously a 1991 massacre of some 2,000 Dinkas by Machar’s forces in the city of Bor. In 2002, he rejoined the SPLM military force; in 2005, after the southern Sudan became semi-autonomous as part of a peace deal, he became vice president—a position he maintained in 2011 when South Sudan became formally independent.

The fault lines remained, however, in what was ostensibly a unity government, as well as within the army, which was formed by bringing together separate militias that had fought under the umbrella of the Sudanese People’s Liberation Army before independence.

The December 15 clash began as an armed confrontation between rival groups of soldiers in the capital, Juba, that quickly spilled over into broader clashes. Kiir claimed that the incident was part of an attempted coup and arrested a number of his rivals within the SPLA.

Forces loyal to Machar claimed on Tuesday that they had recaptured Malakal, but a spokesman for the government dismissed the claim as “mere propaganda,” insisting that its forces had regained control of the city. There were multiple reports of heavy fighting in and around the city.

Fighting has also resumed around the city of Bor in the center of the country, which is apparently still in the hands of the rebel forces. Government troops were reportedly preparing an offensive to seize it.

Machar, meanwhile, told the Sudan Tribune that forces supporting him were preparing a fresh attack on Bentiu, the capital of Unity state—also a center of oil production—from which they had earlier made what he called a “tactical withdrawal.”

Machar also claimed that his forces were fighting not only South Sudanese government troops, but also Uganda People’s Defense Force (UPDF) forces, which have been ordered into South Sudan by Ugandan President Yoweri Museveni on the pretense of protecting Ugandan nationals in the country.

Ugandan attack helicopters have reportedly bombed villages, killing civilians, while Ugandan troops have taken up positions at the presidential palace and the international airport in Juba.

The Ugandan parliament began a debate Tuesday on sending even more military forces into the country, amid criticism by Museveni’s opponents that he had violated both South Sudanese sovereignty with the military deployment and the Ugandan constitution by failing to seek prior approval from the parliament before the first Ugandan units were sent in. Uganda, which shares its northern border with South Sudan, is the country’s largest African trade partner.

The Ugandan intervention underscores the danger of the conflict in South Sudan becoming joined in a wider regional war. Both the Central African Republic to the west and the Democratic Republic of the Congo to the south have been torn by armed conflict. French troops have been sent into the CAR along with Rwandan forces airlifted in by the US.

The US last month also deployed about 50 members of its recently created East Africa Response Force, based in Djibouti, to South Sudan, ostensibly to aid in the evacuation of US personnel.

Even as the fighting continues in South Sudan, talks aimed at achieving a ceasefire are taking place in the Ethiopian capital of Addis Ababa under the auspices of the East African regional bloc, the Inter-Governmental Agency on Development (IGAD).

The US played the major role as the midwife of independent South Sudan, which enjoyed enthusiastic backing from both the Bush and Obama administrations and US constituencies ranging from evangelical Christians to Hollywood liberals. All of them blithely ignored the gross corruption, authoritarianism and bitter divisions that dominated the new state.

Washington, which poured billions of dollars in aid into the South Sudan, saw the creation of the new country of just 9 million people as a means of increasing US influence in the region, particularly against that of China, which was a major trading partner with Sudan. The talks in Addis Ababa, however, have seen the Chinese government take the more prominent role.

China’s Foreign Minister Wang Yi arrived in the Ethiopian capital on Monday to participate in the ceasefire talks. The US representative at the negotiations is Donald Booth, the State Department’s Special Envoy to Sudan and South Sudan.

Since independence three years ago, China has emerged as the new country’s biggest trading partner and foreign investor, accounting for 80 percent of South Sudan’s oil exports. Since the fighting began, production in the largely Chinese-run oil fields has declined by 30 percent, and hundreds of Chinese workers have had to leave the country.