South Sudan marks its third anniversary of independence on Wednesday, with civil war raging, the young nation divided by ethnic atrocities and on the brink of famine.

The streets of the capital have been lined with banners proclaiming "One People, One Nation", with the government of President Salva Kiir due to put on a show of force with a military parade and speeches delivered to celebrate the breakaway from the repressive government in Khartoum.

Authorities have deployed heavy security ahead of the commemorations, underscoring the bitter divisions in the world's youngest nation where a nearly seven-month-old civil war rages on.

"It's a sad anniversary," admitted Juba resident Gideon, 23, saying he had hoped for better three years on from the fanfare and optimism that swept the country in July 2011.

READ: South Sudan: Young nation at the crossroads

At government-organised celebrations in the heart of capital, dance troupes draped in the national flag sang and danced, as drummers banged out beats to shrug off the mood of gloom.

Ugandan President Yoweri Museveni, who has sent in troops to prop up Kiir's government, was one of the few senior regional leaders to attend, with old enemies Sudan sending their second vice-president.

"Let's focus on peace, reconciliation and coming back together... I call on all of you to exert maximum effort to stop the bleeding in our nation," Kiir told the crowds.

South Sudan has been wracked by war since mid-December, when presidential guards loyal to Kiir clashed with troops supporting ousted vice-president Riek Machar, who fled to the bush and rallied a huge rebel army.

The fighting has been marked by widespread atrocities against both members of the Nuer people, to which Machar belongs, and revenge attacks against Kiir's Dinka group, the single largest tribe.

Civilians have been massacred and dumped in mass graves, patients murdered in hospitals and churches, and entire towns flattened as urban centres including key oil-producing hubs changed hands several times.

The most conservative estimates put the toll at 10,000 dead, although aid workers say the real figure is likely far higher. Almost 100,000 civilians are sheltering in squalid camps inside UN bases fearing revenge attacks if they leave.

'Sick' leaders

Aid group Oxfam said South Sudan was "currently Africa's worst crisis with nearly 4 million — a third of the country's population — at risk of severe hunger and an aid effort that has only so far reached half of those in need".

"The world's attention is elsewhere as Africa's worst humanitarian catastrophe descends into more misery. We will be staring into the abyss and fail to avert a famine if funds do not start arriving soon to help the people of South Sudan at risk of starvation, disease and violence," said Winnie Byanyima, Executive Director of Oxfam International.

"If the aid effort does not increase 50,000 children could die from malnutrition. Since the current crisis began in December last year fighting has forced 1.5 million people from their homes and numbers continue to rise."

On the eve of the anniversary, the departing UN representative in the country issued a scathing attack on the country's leaders, calling them a "self-serving elite" responsible for a looming "man-made famine".

"Thousands and thousands have been killed," said Hilde Johnson of the UN mission in South Sudan, lashing out at both the government and rebels, warning that one of world's least developed nations has "been set back decades".

READ: South Sudan will never be saved if everyone continues pointing fingers

Leaders were sick with "the cancer of corruption" with the country's billions of dollars worth of oil "a curse rather than a blessing", she said.

Peace talks in luxury hotels in the Ethiopian capital Addis Ababa have made little progress and last month they halted indefinitely, with both sides refusing to attend the discussions.

"If there are further delays, and the blame games go on, whether from those wanting to remain in office or those wanting to get back in, we can draw only one conclusion; that this is only about a scramble for power," Johnson added.

-AFP-