Long lines of wounded fighters crowd the wards of Bor hospital, the latest casualties of brutal fighting in South Sudan's troubled Jonglei state.
Lying on a basic mattress in a store room -- the surgical ward is too full of those with gunshot wounds -- 15-year old fighter Duol Puol says he went to fight in revenge after Murle fighters attacked his family.
"I should feel sad when we kill them," said Puol, who joined hundreds of young men from the Lou Nuer community in taking up arms against the rival Murle tribe.
"But because my parents have been killed, I feel happy that at least we are paying them back," he adds, as other fellow teenage fighters nod in agreement.
Puol fractured his leg while tumbling into a hole as he fled the larger force of a Murle counter-attack in the Pibor region of Jonglei, in the east of South Sudan.
"If they killed my parents, their parents also need to be killed," Puol added.
More than 100 of the fighters flown in for surgery by the United Nations to the state capital, Bor, have gunshot wounds.
Doctors Without Borders (MSF - Medecins Sans Frontieres) is supporting the basic hospital, and South Sudanese army helicopters are also busy transporting the wounded.
Ruot Mabor, aged just 10, joined older boys in the fight.
"Murle killed all my relatives," Mabor said, explaining why he joined the fight so young. "I knew that Murle could also come and kill me."
Those wounded said they had tried to bury the bodies of many of their comrades, but no one could give exact figures.
All those being treated are from the Lou Nuer tribe, and were airlifted out from one small settlement, the village of Manyabol, fuelling concerns that the number injured or killed elsewhere in the vast region could be far higher.
Access to Murle territory, where there are similar fears of heavy casualties, is extremely limited.
Thousands of Murle are thought to be hiding in the bush, where aid agencies and the UN peacekeeping mission claim they have been unable to provide aid or protection.
Previous attacks in the strife-hit region have seen hundreds, and possibly thousands, of civilians killed.
"Fighting is still going on... they are expecting us to be seeing more (casualties)," hospital director Bior Kuer Bior said, repeating stories told by the wounded who have flooded into wards already at breaking point.
Medical teams who flew to remote Manyabol on Sunday to pick up the most severely wounded were forced to leave before 60 more injured arrived, with gunshots heard in the distance, Bior added.
"There's no way it will end until one side is annihilated," he said.
Tit-for-tat cattle raids and reprisal killings are common in this severely under-developed state, awash with guns left over from almost two decades of civil war.
But the latest upsurge in fighting that began almost two weeks ago is of a different scale and nature, with organised and well armed forces fighting.
Local government officials have reported columns of hundreds -- if not thousands -- of gunmen in tribal militia forces battling in remote and swampy bush.
South Sudan's rebel-turned-official army has also been fighting in the region to crush a rebellion led by David Yau Yau, who comes from the Murle people, since 2010.
"When you go for fighting, killing must happen," said Tut Mut, aged 42, who said he joined the raid to seize back children and cattle he claimed Murle fighters had stolen. "People have died on both sides."
The clashes echo attacks in December 2011, when some 8,000 Lou Nuer marched south killing and looting in what they said were reprisals for earlier attacks and cattle raids by Murle fighters.
The UN later estimated more than 600 people were massacred, although local officials reported the figure to have been far higher.
But Murle youth leader Paul Kuakuak, speaking in the capital Juba, claims that the Lou Nuer militia is backed by the government, an accusation strongly denied by officials who say the army is supporting neither side.
"Those people who came and attacked Murle are not youth, they are militias that have mobilised by the state," said Kuakuak, saying that only wounded Nuer have been taken to hospital.
Those wounded say they want the fighting to stop, yet at the same time few seem able to break a bitter cycle of revenge.
"If they don't stop, neither will we," said Puol, views echoed by his comrade Mut.
"If the Murle are protected and the authorities tell us to go back, we will still come back, until this is settled once and for all," Mut said.