At least 150 US Marines are on alert, ready to enter the increasingly violent and chaotic situation in South Sudan. The troops are moving from Moron, Spain, to the Navy's Camp Lemonnier in Djibouti.

Their mission will be to evacuate American citizens and help protect our diplomats.

CNN:

"By positioning these forces forward, we are able to more quickly respond to crisis in the region, if required," read a statement from U.S. Africa Command.

It cited the example of Benghazi, where an attack last year killed U.S. Ambassador Christopher Stevens and three other Americans.

"One of the lessons learned from the tragic events in Benghazi 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," the statement read.

According to a senior administration official, 380 American citizens and about another 300 third-country nationals have been evacuated.

"Based on registration, there are American citizens in other towns and areas throughout South Sudan. We are trying to track down how many may still be there. Many may have gotten out on their own. We are trying to track that down," the official said.

On Sunday, all Americans who presented themselves at a U.N camp in the flashpoint town of Bor were evacuated safely, the State Department said.

A State Department official said about 15 Americans were flown out Sunday. U.S. personnel have been working to confirm that no other U.S. citizens remained in Bor in need of evacuation.

U.N. civilian staff were moved from a compound in Bor to Juba, the capital, on Saturday, the same day a U.S. mission to airlift Americans out was aborted when the aircraft came under fire.

Four U.S. troops were wounded in the attack in Bor and were to be moved to the U.S. military hospital at Landstuhl, Germany, a senior U.S. official told CNN on Sunday.

One of the injured "went through some pretty serious surgery" after being taken to Nairobi, Kenya, with wounds from gunshots fired at the aircraft. All four have been able to speak to their families.

"The United States and the United Nations, which has the lead for securing Bor airport in South Sudan, took steps to ensure fighting factions were aware these flights were a humanitarian mission," State Department spokeswoman Jen Psaki said in a statement.

Things are getting out of control in South Sudan. There are now reports of massacres, mass graves, rape, and it's getting worse. A refugee crisis is brewing as tens of thousands flee the ethnic cleansing underway.

South Sudan could easily become another Somalia - a failed state run by gangs and warlords who target the innocent. Will the world stand by and let it happen again?

Of course we will. No one wants to get their hands dirty so the butcher's bill will continue to rise:

On Dec. 15, fighting erupted in Juba that has swiftly spread beyond the capital along ethnic faultlines, exposing the failure of national reconciliation efforts, the limited influence of generous foreign sponsors and the reluctance of rebel fighters-turned-statesmen to give up the tactics of bush conflict.

Whether South Sudan tips into a broader ethnic war or draws back from the brink largely depends on two men who have long tussled for power: the president from the dominant Dinka tribe and the ambitious deputy he sacked in July, Riek Machar, a Nuer.

Both ethnic groups, spurred on by their leaders, have clashed in the past, giving the latest spiral of violence an air of depressing inevitability for many South Sudanese, desperate for development in one of the poorest places in Africa.

"Neither cares much about their people," said Chuo, who repairs motorbikes in Juba. "Instead, they are focusing too much on personal grudges - the left-overs from their old days."

The United States and other Western backers of the new nation are scrambling with regional African states to broker talks, but have limited leverage to end fighting that has killed hundreds of people and driven 40,000 to U.N. bases for shelter.

Failure to halt the escalation could have wider fallout in an already volatile region. Sudan may be drawn in if there is a threat to oil fields from which it derives vital fees from pumping crude across its land. And other neighbours fret about a descent into chaos. Uganda has already sent troops to Juba.

Both leaders say they are ready to talk. But old habits die hard. Kiir said he was the target of a "foiled coup" and rounded up rivals. Machar slipped away and has mustered militia forces.

The UN will vote later today on whether they should send 5,500 more "peacekeepers" to the country. That's 5,500 more targets for the combatants.

No doubt, the UN will send a "strongly worded letter" to the two men.