Violence in South Sudan's capital of Juba has killed scores of people this week in what first appeared to be an attempted coup. But the man the government has blamed for inciting the clashes -- former Vice President Riek Machar -- said Wednesday that he was not behind any attempts to overthrow the administration of President Salva Kiir, indicating that the turmoil is instead rooted in longstanding ethnic rivalries in the world's youngest country.

“There was no attempted coup,” Machar told the BBC, adding that the president was “inciting tribal and ethnic violence” and should step down.

Gunfire reportedly broke out Sunday evening in a military barracks, and Kiir claimed it was incited by members of the presidential guard loyal to Machar, who was relieved of his post in July after accusing Kiir of “dictatorial” behavior. But their rivalry runs deeper than politics; Kiir is a member of the Dinka ethnic group, which is South Sudan's most populous and has been accused of monopolizing power. Machar is from the Nuer group, the country's second-most populous. Nuer communities are prominent in Unity State, one of South Sudan's most oil-rich areas.

Clashes between factions of the ruling party, the Sudan People's Liberation Movement, are nothing new. Even when the SPLM was a rebel group loosely united in the fight against northern Sudanese forces, Dinka-Nuer tensions ran high. One 1991 attack in the northern town of Bor, largely perpetrated by Nuer militants against Dinka people, killed hundreds and raised tensions that persisted even after South Sudan split from its northern neighbor.

This week, the Juba administration has arrested at least 10 people, including ex-officials, and is in pursuit of Machar, whose exact whereabouts are unknown. Death toll estimates have ranged from 40, as reported Tuesday by South Sudan's Health Ministry, to at least 400, according to reports the U.N. received from local sources. Up to 20,000 Juba residents have fled their homes to seek respite at nearby U.N. military bases, and many of the refugees are Nuer people. But some analysts warn that ethnic fault lines are not entirely to blame, and are instead being manipulated by various factions seeking power.

“Many Dinkas are being arrested as well. The Dinkas are not unified and there is no strong solidarity within the SPLM politicians,” said Cedric Barnes, Horn of Africa project director at the International Crisis Group, to France24. “It’s being manipulated by all sides and people are instrumentalizing ethnic identity to achieve political ends.”

South Sudan has gotten off to a rocky start since it formally achieved independence following a public referendum in 2011. It came away with three-fourths of the formerly united countries' oil reserves, but the pipeline and refineries needed to get that crude to market remain in Sudan's possession. Both countries rely heavily on oil for the vast majority of national revenues, but a row over transport fees and border disputes led to a 14-month production shutdown beginning January 2012, devastating both economies. Oil has been flowing since a March agreement was brokered by the African Union, though output is now down to about 200,000 barrels per day, from about 350,000 barrels before the shutdown.

Mutrif Sideeg, Sudan's ambassador in Juba, said the clashes there would not necessarily threaten the agreement since the conflict is “an internal situation from which the South is suffering,” according to the Sudan Tribune. "I confirm that the process of cooperation will not be impacted, but we will be working to have it proceed as planned as soon as things return to normal," he added.

Clashes in Juba appear to have died down from their high point early this week, but some of the violence spilled over into Bor on Wednesday, threatening to turn South Sudan's political rivalry into a diffuse and increasingly unpredictable conflict.