More than 1 million disabled people are vulnerable to the increasing violence of South Sudan's brutal civil war.

Mary Nyakwas lost her leg to a crocodile while fleeing the fighting. She and her four children had taken refuge from the conflict in a nearby swamp when the reptile attacked her.

Now the 30-year-old sits on the floor of her hut in a civilian protection camp in Bentiu, running her finger over the curve of her stump. Nyakwas relies on friends and neighbours to bring her water and food. Without them, she says, she'd starve.

"I can't do anything for myself now," she says.

When clashes break out, South Sudan's disabled and elderly are often unable to flee and are sometimes shot, hacked to death or burned alive, according to a new report by Human Rights Watch.

The disabled and older people "find themselves at much greater risk of starvation or abuse," the Human Rights Watch report said, urging the United Nations and aid groups to do more to assist the vulnerable.

As South Sudan's civil war moves well into its fourth year, aid workers are struggling to meet the needs of 1.9 million internally displaced people. An estimated 250,000 are disabled and living in UN civilian protection sites across the country, the World Health Organization says.

Even in the camps, many end up living in squalor with little assistance.

Nyakwas has been offered some help. The International Committee of the Red Cross planned to fly her to the capital, Juba, so she could be fitted with a prosthetic limb. But she didn't want to leave her children behind.

The ICRC says it is looking into creating small mobile units to operate in more remote areas of the country. But because of a recent increase in fighting, the organization has put such projects on hold.

The UN humanitarian agency said many aid groups are trying to respond to the needs of the disabled and elderly. It also called on all parties in the conflict to spare the most vulnerable from the "scourge of war." 

Another young South Sudanese woman, Nyang Maria, has never been able to use her legs, but she says life was easier before she came to live in the Bentiu camp.

As she can't stand up, the 19-year-old is forced to sit on the camp's filthy latrines, which are rarely cleaned and full of feces.

"Before, I could go to the bathroom anywhere," Nyang says. "Here, there are just a few toilets and they're all full of disease." 

In order to increase her mobility, the International Organization for Migration gave her a special-needs tricycle, but she says the tires keep bursting because of the camp's gravel roads. It now sits idle in the corner of her home. She lies limp on the floor beside it.

"Why?" she says, tears streaming down her face. "Why did God make me this way?"