RIER, UNITY STATE, southern Sudan - Hardly 30 minutes after restaurant owner William Makwach described Rier as a peaceful, progressive trading centre, the village turned into something like a war zone.

Gangs of spear-throwing young men chased each other through the streets. Traders shuttered their shops and women and children scattered to safety.

"For how long shall we suffer?" asked a woman holding a toddler.

The woman was a recent returnee to Rier in the flashpoint border area between northern and southern Sudan. She'd spent seven years in Ethiopia as a war refugee, one of some 4 million people uprooted by 21 years of conflict between north and south that killed around 2 million.

The war ended with a fragile peace deal in 2005, but smouldering violence between rival tribes and clans means life is anything but peaceful for those who have made the long journey home.

The violence is not directly related to north-south divisions, but it thrives in an area left lawless by years of war and neglect from both Khartoum in the north and Juba in the south

In April alone, tribal clashes claimed more than 200 lives in Joglei State, while ethnic violence has been reported across the oil-rich region. Meanwhile, disease and hunger stalk thousands in this harshest of landscape.



Tens of thousands of refugees have been streaming back since late 2005, but the U.N. refugee body, UNHCR, is now warning that a deteriorating security situation in several parts of southern Sudan is hindering further returns from Uganda, Kenya and Ethiopia.

Several towns in Central and Eastern Equatoria states were paralysed in March by coordinated blockades organised by veterans from the Sudan People's Liberation Army, south Sudan's former rebel force, who had not been paid benefits for five months.

Aid workers say insecurity and worsening food shortages are now driving many returnees to the brink of despair.

ILLEGAL ARMS AND TRIBAL WARS

While Rier's clashes left five people wounded, other outbreaks of violence have proved far more deadly.

Fighting between two ethnic groups in Akobo in Jonglei State reportedly killed 250 people in late April. Mud Huts were burnt and food stocks destroyed.

"The main problem in these areas is that there are so many illegal arms, and now people are using them to make ends meet," said William Malwal, director general of Koch County in Unity State on the border or north and south.

High school teacher and former refugee Bill John Awat attributed the increasing violence to post-war trauma and a failure to disarm various militia groups after the war.

"Though the war ended four years ago, it remained in people heads," he said. "Many people think they can get everything they want through violence, and that will a long time to change."

Medecins Sans Frontieres (MSF), the only medical relief group present in many areas of south Sudan, is grappling with the task of treating the wounded from warring groups, on top of increasing cases of diarrhoea, dysentery, Sleeping sickness, malaria and malnutrition.

"The fighting is mainly affecting women and children," said Colette Adenne, the agency's head of mission for southern Sudan. "I treated a mother whose baby had been shot in the arm. She told me many children had been killed in the fighting."

MSF is treating 36 people wounded in last month's fighting in Akobo.

"When fighting takes place there is immediate massive displacement, which, if it does not stop, could worsen the humanitarian situation," Adenne said.

Though tribal conflicts over water and land are not new in Sudan, there is growing concern that the sheer number of arms in circulation among a population brutalised by years of war is taking the violence to tragic new levels.

In a statement last week, the U.N. mission in Sudan, UNMIS, called on "all sides to suspend violence and asked the tribal and community leaders to resolve their differences by means of peaceful negotiations, in compliance with the 2005 Integral Peace Agreement".

Similar calls have come from the semi-autonomous government of southern Sudan, but have so far done little to ease tensions.

FLOODS AND HUNGER

Against a backdrop of shattered infrastructure, severe unemployment and extreme weather, many former refugees described life as getting worse by the day.

"Last year I lost my son to malaria," said Regina Agwak, a 46-year-old mother of four. "Since we returned we have no access to medical services, no clean water and not enough food."

Most northern parts of southern Sudan have suffered devastating floods since 2007 that have destroyed crops and washed roads away.

In late April, large swathes of Unity State along the River Nile lay completely under water, with entire communities cut off for weeks. Roads were unusable and food stocks were ruined.

"Even if we decide to till this land, it is either too waterlogged or too dry to grow anything," Agwak said.

Floods and other extreme-weather events mean that thousands of people uprooted by the recent ethnic violence have no way to find sustenance or even basic shelter.

As the region braces for national elections in 2010 and a referendum on southern succession the following year, aid agencies say the outlook for many remains one of fear, hunger and hardship.

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