U.S. and African officials seeking to mediate an end to South Sudan’s bloodshed are, in effect, trying to repair rifts in the very liberation movement that they supported for years. The conflict, which pits powerful tribes against each other, is also a political struggle that threatens to shatter one of the continent’s most storied groups of freedom fighters.

After South Sudan won independence from Sudan in 2011, U.S. diplomats and analysts expected that lingering animosities over oil revenue, disputed boundaries and security would be the biggest challenges facing the world’s newest nation. Instead, it is the leaders Washington nurtured who threaten to unravel one of America’s most significant policy successes in sub-Saharan Africa in this century.

Consider this: Many of the 11 senior South Sudanese officials arrested for an alleged coup attempt nearly two weeks ago belong to President Salva Kiir’s ethic group. Like him, they are stalwarts of the Sudan People’s Liberation Movement, now the ruling party.

“There may be elements who seek to exploit the current crisis to pursue their own agendas, but this is fundamentally a power struggle,” said Hilde Johnson, the top U.N. official in South Sudan.

Ethnic bloodletting between South Sudan’s two largest tribal groups — the Dinka and the Nuer — is raging in many parts of this vast oil-producing nation, raising fears of a potential civil war. Yet the tussle for power in the political realm is more complex. Some of Kiir’s most vocal opponents are, like him, Dinka. And there are Nuer politicians who oppose Riek Machar, the former vice president and a Nuer, whose loyalists are waging a rebellion against the U.S.-backed government.

In many ways, the political tensions reflect the SPLM’s struggles as it transitions from band of fighters to ruling party in a new democracy infused with billions of dollars in oil revenue.

“Those who came as liberators are now the ones fighting themselves,” said Jok Justin Ayoch, an opposition party leader. “They are very irresponsible, inexperienced and incapable to learn. If you are in power for eight years and you cannot agree between yourselves, that only brings chaos.”

The SPLM has been a political force since 2005, when it signed an American-backed peace accord with the Khartoum government that ended Sudan’s 22-year-long civil war, paving the way for independence 2½ years ago. But within six months of independence, ethnic, tribal and political tensions had triggered violent clashes in several regions.

Successive American administrations have invested billions of dollars in hopes of making South Sudan an oasis of stability in a region plagued by growing Islamist militancy and terrorism. It was a cause that united disparate groups of Americans: Democrats and Republicans, people of different faiths, and human rights activists. African nations such as Kenya and Ethiopia, which are now leading mediation efforts, were also among the SPLM’s biggest backers.

The current clashes were triggered by a dispute, followed by fighting, between soldiers loyal to Kiir and Machar on Dec. 15. That grew into allegations by Kiir that Machar was trying to seize power and led to the arrests of the 11 officials. Within days, fighting had spread to half of South Sudan’s 10 states, including vital oil-producing areas. Several thousand people have been killed, according to U.N. officials, and more than 100,000 have been uprooted from their homes as aid agencies tackle a burgeoning humanitarian crisis. Dinkas and Nuers are accused of perpetrating atrocities against each other.

On Friday, African leaders meeting in neighboring Kenya reportedly declared that South Sudan’s government had agreed to a truce and called on Machar to make a similar pledge. But fighting raged on in Malakal, the capital of oil-rich Upper Nile state, with the government and the rebels claiming they controlled the town.

Echoes of a long-ago split

The SPLM and its armed wing, the Sudan People’s Liberation Army, has for more than two decades been an unruly conglomeration of ethnic groups and militias, beset by fractious divides. The most famous split took place in 1991 when Machar left the movement. He joined the Khartoum regime six years later and then returned to the SPLM in 2002.

But the rivalry between Kiir and Machar only intensified, especially after the death of SPLM leader John Garang in a 2005 helicopter crash that propelled Kiir to the leadership.

Late last year, Machar declared his intention to contest the chairmanship of the SPLM, held by Kiir, a position that could have led to Machar achieving his core ambition: becoming president.

Analysts say there was intense resistance to Machar’s decision to run, particularly from Kiir’s inner circle, made up of his clan of Dinka tribesmen. They had not forgotten the 1991 split, which triggered violence that included the massacre of hundreds of Dinka by Nuer soldiers, which human rights activists and SPLM officials have linked to Machar.

“Within the party, Salva Kiir has found growing discontent with his style of leadership, and this may have forced him back on relying increasingly on his home community both within the party and within the security forces,” said Douglas Johnson, author of “The Root Causes of Sudan’s Civil Wars.” “As for Riek, support for him by various Nuer communities has not been uniform or consistent.”

By this past spring, Machar was openly questioning Kiir’s ability to govern the SPLM and the nation. In April, Kiir stripped Machar of many of his powers. Three months later, he fired Machar from his position as vice president and dissolved the cabinet. He also suspended Pagan Amum, the SPLM secretary general and a popular nationalistic figure, accusing him of corruption.

Late last month, Kiir reportedly sought to dissolve key SPLM structures that determined the party’s leadership, a move his critics say was an attempt to consolidate his power. On Dec. 6, Machar, Amum and other ousted officials declared that Kiir had dictatorial tendencies and that he had “immobilized” the SPLM, driving it and South Sudan “into the abyss.”

Ten days later, the clashes began.

‘We will pursue them’

At a news conference Friday, Information Minister Michael Makuei Lueth denied the allegations against the president, point by point.

He said that if the ousted officials “knew Salva was a dictator, why did they continue to be in his government? These people want to come up by force. They want to overthrow a democratically elected government.”

Some of the ousted officials are among those arrested after the coup attempt. Lueth vowed that Machar and other loyalists who had gone “into the bush” will be “hunted down” if they don’t come to the negotiating table.

“We will pursue them because we were in the bush, all of us,” Lueth said.