Two-year-old Islam Musa lay in the corner of bed number six as her grandmother, Zena Bade, fed her milk through a tube.

Stalked by hunger and aerial bombardment, the pair were among the tens of thousands of people who have been driven from their home in Sudan's Blue Nile state across the border into South Sudan's Doro refugee camp. For months, Bade said, they had survived on nothing but leaves and tree roots.

"The government soldiers came and chased us away from our village and took away our sorghum," she said, speaking in the white medical tent where her granddaughter lay. "We hid in the bush."

Their plight encapsulates the human toll of a war that has convulsed Sudan's border states since South Sudan became an independent country over the summer, throwing a spotlight on a conflict that is complicating efforts to resolve issues such as oil revenue sharing between Sudan and the South.

Sudan's division initially overshadowed the fighting, but warnings of impending famine from the United States and activists such as Hollywood actor George Clooney have refocused attention on the conflict.

Limited access to the border regions makes it hard to accurately assess the war's impact. But the United Nations estimates that over 410,000 people have fled their homes in Blue Nile and South Kordofan, another border state.

Aid workers and refugees in Doro camp, where some 45,000 people have fled, say food stocks in Blue Nile are likely to run out in the next couple of weeks.

"The area is a war zone now. The traders are not going there. There is not anything coming from outside. What the people have there now is finishing," Doro camp supervisor Sila Musa said, standing in the baking sun. "They depend on the roots of the trees and the fruits of the trees."

Musa, former commissioner of Kurmuk county in Blue Nile, estimated that up to 100,000 people may be trapped in the state, unable to leave because they cannot carry the food and water they would need for a journey that can take as long as a month.

Like many of Khartoum's critics, he said the bombing campaign was deliberately designed to cause hunger, scatter civilians and deprive the guerrillas of a support network.

"It becomes just like a weapon because if people do not eat, they are going to die. The same as if you are using a gun, you are going to kill the person. There is no difference," he said.

Sudan regularly denies such charges, saying the armed forces are working to protect civilians and that it is the rebels who have been responsible for any humanitarian suffering. Khartoum has also dismissed fears of a looming famine. Daffa-Alla Elhag Ali Osman, its UN ambassador, has described the humanitarian situation in South Kordofan and Blue Nile as "very normal."

Last week, the United Nations said it had made some progress in talks with Sudan to deliver more aid to South Kordofan, but said it wanted more access.

Bombardment in Blue Nile and dire conditions in the refugee camps have pushed many young men to consider joining the rebels.

"There is nothing left there," Nathanial Yahia, 26, said, squatting in the dust to play Bau, a game using stones and a board hewn from the back earth. "We young people, we are now very angry because our mothers and fathers are not in a good situation."

He described his fields across the border, where he said Antonov aircraft bombed day and night. "Because of the Antonovs, everybody now wants to help the rebels, so that they can fight together, so that the people can go back home to Blue Nile state. Living here is not free."

As with most of Sudan's conflicts, the roots of the wars in Blue Nile and South Kordofan stretch back decades. Tens of thousands of fighters in both states sided with the south during a civil war against Khartoum that started in 1983.

A 2005 peace deal ended the fighting, clearing the way for Sudan's partition in July, but it left the two states in the north. The pact offered residents of the states "popular consultations" to determine how they would interact with Khartoum, but those talks were never completed.

In June, the Sudan People's Liberation Army-North (SPLA-N), made up of a former division of the southern rebel army, began fighting government forces in South Kordofan. Other SPLA-N troops loyal to Blue Nile Governor Malik Agar quickly took to the bush when fighting spread to that state in September.

Khartoum and Juba have repeatedly accused one another of backing rebels on either side of the border since then, hindering talks over unresolved issues such as how much the landlocked South should pay to use oil infrastructure in Sudan.

The talks became more urgent in January, when Juba shut down its output of about 350,000 barrels per day after Khartoum began siphoning off some oil to make up for what it called unpaid fees. Crude production is the lifeblood of both economies.

South Sudan has since accused its northern neighbour of "stealing" over six million barrels of crude and of bombing an oil well close to their shared border, which Sudan denies doing. After months of rancour, the two presidents are set to meet next month to try to break the deadlock.

Analysts say any deal will hinge on the two sides agreeing to end what they describe as proxy wars that have displaced tens of thousands of people like Islam and her grandmother. There appears to have been some recent progress at the talks, which have repeatedly collapsed in acrimony, though Sudan watchers are cautious about raising hopes of a deal.

"I don't think they would be going ahead with the summit if there wasn't some forward momentum on the outstanding issues," said Aly Verjee, an analyst at the Nairobi-based Rift Valley Institute think tank.

Actor George Clooney was arrested in front of Sudan's embassy in Washington DC last week, as he sought to draw attention to the bombing campaign.

Some activists have praised the celebrity for publicising a conflict that remains obscure for many Westerners. But others have criticised what they view as his oversimplified depiction of the conflict as Sudan's ruling Arab elite targeting black Africans.

There are also concerns that Clooney's activism, which is aimed at getting the United States to pressure Khartoum into ending the "man-made tragedy," could damage talks at a critical stage by making it harder for Washington to help broker a deal.

Whatever the impact of celebrity activism, international awareness has come too late for Islam Musa in bed six.

Three days after the interview with her grandmother, she died, becoming another statistic on the whiteboard of the Doro refugee camp.