Continued armed clashes, mass killings, "spiraling violence" and tens of thousands of displaced people have led some to wonder if the world's youngest country is on the brink of civil war.

The newest wave of violence erupted in oil-rich South Sudan, an independent nation since 2011, on Dec. 15, when, as the Guardian reported,

South Sudan's president, Salva Kiir, has accused his former deputy Riek Machar of attempting to launch a coup [...] The pair, who have been rivals since the long civil war that ended in 2005 and split the country, had been in an uneasy power-sharing government since independence in 2011.

Kiir hails from the Dinka community, while Machar comes from the Nuer. The accusation that the former vice-president had attempted to seize power led to widespread reprisals against his supporters and fellow Nuer in the capital and surrounding areas. What began as a political power struggle has spilled over into open ethnic conflict in some areas.

The BBC's South Sudan analyst James Copnall cautions against painting the conflict as simply one of ethnic divisions:

The growing number of allegations of ethnically motivated killings are deeply concerning. It's important to remember that this crisis is at its heart a political struggle, in a militarized, and, yes, ethnically divided society.

The strength of politicians often comes from their ethnic base, so the power struggle is exacerbating ethnic cleavages.

It is wrong to paint this as an "ethnic war", though - it is far more complicated than this. It is also unclear to what extent the military commanders can control the many armed civilians fighting in different parts of the country.

On Monday, UN Chief Ban ki-Moon asked the Security Council to send up to 5,500 more troops to the country, while UN human rights chief Navi Pillay warned Tuesday of mass graves and "palpable fear" amongst civilians.

“Mass extrajudicial killings, the targeting of individuals on the basis of their ethnicity and arbitrary detentions have been documented in recent days,” Pillay said. “We have discovered a mass grave in Bentiu, in Unity State, and there are reportedly at least two other mass graves in Juba.”

“There is a palpable fear among civilians of both Dinka and Nuer backgrounds that they will be killed on the basis of their ethnicity,” Pillay added. “There need to be clear statements and clear steps from all those in positions of political and military control that human rights violations will not be tolerated and those responsible will be brought to justice.”

The European Union's foreign policy chief, Catherine Ashton expressed concern over the violence as well. "I am extremely concerned that South Sudan risks spiraling into a disaster for both its own people and the region," she said on Tuesday. "Such a situation can, and must, be avoided."

U.S. military forces are ready to intervene, with 150 Marines now in Djibouti, according to Africa Command.

"By positioning these forces forward, we are able to more quickly respond to crisis in the region, if required," said the Africa Command.

"One of the lessons learned from the tragic events in Benghazi [Libya] was that we needed to be better postured, in order to respond to developing or crisis situations, if needed. These precautionary movements will allow us to do just that," it said.

U.S. military aircraft has already been under attack in South Sudan while carrying out an evacuation mission.

While foreign nationals have been evacuated, tens of thousands Dink and Nuer have been forced to flee, displaced within their own country.  51-year-old Peter Bey, a Nuer, has watched foreign nationals escape to safety as he, and many others, seek shelter at a UN mission base in Juba.

"We see from history that the UN has left people behind before in Rwanda," Bey said. "They put their own people on helicopters and left the people who died."

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