The United States -- a key backer of South Sudan's 2011 independence -- is increasing diplomatic pressure amid an intensifying conflict there but will not consider military intervention, experts said.
Analysts do not expect Washington to launch a massive military campaign, despite President Barack Obama's decision to send nearly 100 troops to the country this week to help protect US citizens, personnel and property.
Obama has warned South Sudan over the week-old conflict, saying the country was on the "precipice" of civil war and that any military coup would trigger an end to diplomatic and economic support from Washington and its allies.
Secretary of State John Kerry also told President Salva Kiir over the weekend that the violence endangers the independence of the world's youngest nation, born in July 2011 after a five-decade struggle for independence from Sudan.
Fighting has gripped South Sudan since December 15, after Kiir accused his former deputy Riek Machar of attempting a coup. Machar denied the claim and accused Kiir of carrying out a vicious purge of his rivals.
Washington has had a longstanding interest in South Sudan and supported the southern rebels in their battle for independence.
Post-independence, the United States became Juba's biggest source of political and economic aid as the country took its first steps, recalled Richard Downie, Africa assistant director at the Center for Strategic and International Studies.
"Now the US is looking at the situation, and it is driven by this desire not to let all the hard work get away," the analyst said, noting that Washington's engagement in South Sudan has been "driven by humanitarian concerns."
Strategic vs humanitarian motivations
Downie recalled that throughout president George W. Bush's 2001-2009 tenure, there were "ongoing efforts diplomatically to try bringing peace to Sudan" that begun as a bid to end the bloody, long-running civil war between the North and the South.
Also lobbying for sustained US involvement were South Sudanese living in the United States, many of whom are devout Christians and have the support of the US evangelical movement.
And the fate of South Sudan has long interested Hollywood -- with actors George Clooney and Mia Farrow in particular taking up the cause.
Washington was one of the forces behind the January 2005 peace agreement in Naivasha, Kenya that ended the civil war, offering six years of autonomy for the South and a referendum in January 2011 to decide on independence. The South Sudanese overwhelmingly voted to break away from Khartoum.
"When the referendum was being held on independence, the US got engaged diplomatically again, and putting resources in to make sure that referendum happened and South Sudan achieved its independence," Downie said.
Obama's National Security Adviser Susan Rice, who has worked on the Sudan issue for 20 years including in her previous post as UN ambassador, repeated calls for all parties to help end the conflict in an audio message to the country.
Rice and her successor at the UN Samantha Power have been impacted by the wars in Bosnia, Darfur and Rwanda, and by what they see as flawed US responses.
But offering a more cynical take was France's former ambassador to Khartoum Michel Raimbaud, who said he "doubts that democracy and human rights guide the interests of the United States in South Sudan."
"The secession, in which Washington played a very important role, was motivated by oil and strategic considerations, to break up Sudan -- the biggest Arab country in Africa," accused the retired diplomat who now works as an independent expert.
Downie contested these allegations, saying Americans are "not involved in the oil industry there very much at all," and "there is a very thin strategic interest in South Sudan."
The Obama administration quickly sent to Juba its envoy for Sudan and South Sudan, Donald Booth, and deployed 45 troops to reinforce security for Americans staying there after the evacuation of some 380 US officials and private citizens.
But Downie doesn't expect Washington to engage militarily in any major way.
"It would require a big leap for the US to get involved significantly on the military level," he said.
"Look across Africa, the US military is very, very wary of getting the boots on the ground."