As South Sudan slid toward civil war, President Barack Obama warned Saturday against “any effort to seize power through the use of military force.” In an earlier statement, Obama said South Sudan was “at the precipice” and added that the “fighting threatens to plunge South Sudan back into the dark days of its past.”

The country was carved out of Sudan less than two-and-a-half years ago with Washington’s full support. Despite its oil wealth, the landlocked and impoverished country remains heavily dependent on US and other international aid.

Washington’s warning followed the Pentagon’s dispatch of 45 US troops to the South Sudanese capital of Juba to secure the US embassy and assist with the evacuation of US nationals and others from the violence-wracked country.

It coincided with an incident in which US warplanes were fired upon by rebel forces, wounding four American military personnel, one of them seriously. The incident took place in Bor, the capital of eastern Jonglei state, which has been at the center of the fighting between forces loyal to US-backed President Salva Kiir and those backing his ousted former vice president, Riek Machar.

Kiir is from South Sudan’s Dinka ethnic group, the country’s largest (approximately 15 percent), while Machar is an ethnic Nuer, the second largest community (approximately 10 percent). While backers of both men are drawn from various groups, the fighting has increasingly taken on an ethnic dimension, with reports of attacks on civilians by ethnic-based gangs from both sides.

Bor fell to rebel forces backing Machar last week, and reportedly the rebels mistook the US aircraft—Ospreys, designed to take off and land like helicopters and fly like planes—for Ugandan aircraft backing government troops.

Uganda has sent hundreds of its own troops into South Sudan, and there have been reports of bombings by Ugandan warplanes, which the Ugandan government denies.

Thousands have been killed or wounded in the fighting, and tens, if not hundreds, of thousands driven from their homes, many of them crowded into United Nations peacekeeping bases for protection. An attack on one of these bases last Thursday by what UN officials described as “unknown assailants” killed three Indian peacekeepers and 11 civilians.

Obama’s warning against any military seizure of power strongly suggests Washington support for Kiir’s thoroughly corrupt and authoritarian government and its claim to be responding to a coup attempt. Backers of Machar, however, dispute this claim, insisting that the nationwide fighting began as an armed clash within Kiir’s presidential guard between Dinka and Nuer soldiers, which ignited tensions that have been simmering since Kiir sacked Machar and over half his cabinet last July. Fighting spread in the capital of Juba and then across the country.

Machar and his supporters charge that Kiir seized on the fighting as a pretext for a military crackdown aimed at liquidating all of his political opponents. Machar, who had vowed to challenge Kiir in an election set for 2015, has demanded that Kiir step down, insisting that he has “repeatedly violated the constitution and was no longer the legitimate president.”

The Financial Times reported that the home of Rebecca Garang, the widow of the founder of the modern South Sudanese separatist movement and a former minister sacked by Kiir, was surrounded by government troops, who opened fire from all sides. Under house arrest, she had joined with Machar Pagan Amum, a former secretary-general of the ruling party, and other senior politicians in charging Kiir with employing “dictatorial tendencies” that threatened to “create instability in the party and in the country.”

The Financial Times cited unnamed Western diplomats and security experts as disputing Kiir’s charge of a coup, which has apparently been embraced by the Obama administration. “This was not a coup attempt, but a move by the president to round up potential plotters and challengers,” it quoted one “foreign observer” as saying. “It certainly looks like Salva Kiir’s night of long knives.”

The position of the government appeared more precarious Sunday after it acknowledged that it no longer controls the northern city of Bentiu, the capital of the key oil-producing state of Unity. The commander of the Fourth Division based there, General James Koang, disbanded the local government, declaring himself the military governor and backing Machar. Loyalist troops were overwhelmed and driven out of the city. According to reports from South Sudan, rebel forces have already begun taking over at least some of the state’s oil fields.

At least 16 oil workers have been reported killed in fighting in Unity state, and China National Petroleum Corporation, the largest oil producer operating in South Sudan, is attempting to evacuate its personnel.

The government’s loss of this oil-producing region raises the prospect of it being cut off from its main source of funding. It also increases the threat that Sudan, to the immediate north, will become involved, as it too relies on revenues from the delivery of South Sudanese oil via a pipeline to Port Sudan on the Red Sea.

The country is a focal point for broader geo-political conflicts. Washington was the key supporter of South Sudanese separatism. It was the lead power in brokering a 2005 Comprehensive Peace Agreement to end a more than-two-decade-long conflict that had claimed more than 2 million lives, setting the stage for the establishment of South Sudan as a separate country.

The main motive for US machinations in the region was to weaken China, which had established close economic and political relations with the government of Sudanese President Omar al-Bashir. More than 60 percent of Sudan’s oil was exported to China, which was the largest shareholder in the two major oil consortiums operating in the country. It also was Sudan’s major supplier of arms.

Since 1997, Washington has maintained economic sanctions against Sudan, claiming that the government in Khartoum is a “state sponsor of terrorism” and “poses an extraordinary threat to the national security and foreign policy of the United States.” The US played the principal role in pushing through war crimes charges against al-Bashir at the International Criminal Court, whose authority Washington itself refuses to recognize.

The formation of the US military’s African Command, or Africom, was heavily bound up with the US bid to supplant Chinese influence in the region, and in Sudan in particular. South Sudan has been discussed as a possible base for Africom.

While the deal to split Sudan—previously Africa’s largest nation—in two left South Sudan with the lion’s share of the territory’s oil wealth, the US bid to supplant China’s dominance in this field has proven less successful. Despite its alignment with Washington and political hostility over Beijing’s close ties with Khartoum, the regime in South Sudan has allowed China to maintain its role as the largest oil producer—followed by Malaysia and India—in part because of its offer of loans and infrastructure projects that Western energy conglomerates cannot match.

Ironically, Washington’s maintenance of Khartoum on its list of state sponsors of terrorism has stymied any significant role by US companies in South Sudan, as Sudan receives a share of the profits from South Sudanese oil deals.

Given US imperialism’s stake in South Sudan and its increasing reliance on military superiority to offset economic challenges from rivals like China, there is a real threat that the present internal conflict can become the pretext for a US “humanitarian” intervention. Any such military operation would inevitably further inflame the high level of tensions generated by the Obama administration’s “pivot to Asia” and the advanced preparations in the Pacific for a military confrontation with China.