Hawa Abdullahi’s father pulls back her orange shawl to show where a bullet smashed through her upper arm. The 15-year-old girl is in pain and traumatised, but in her family she is the fortunate one. Four of her brothers are dead after an attack they blame on the Janjaweed. “Maybe God knows why this happened,” said Maryam Ayacoub Solomon, the mother of the murdered boys. “I don’t know. I don’t know what to say — I have no words left.”

Every few days, more refugees from Darfur cross the border into eastern Chad. They all tell the same story; in recent days and weeks, there have been fresh attacks on black African villages involving Janjaweed fighters backed up by Sudanese government troops.

Despite a UN security council resolution demanding that Sudan disarms the Janjaweed, Khartoum’s war against its own people goes on.

UN officials say that 11 villages close to the border with Chad are believed to have been cleared in a campaign that began a few days after the security council resolution was passed.

Nearly 500 refugees have been registered by the UN after crossing the border at Senett, near the village of Birak in eastern Chad.

Abdel Moula Abdullahi, 25, told the Guardian he had escaped an attack on Diba village in west Darfur on August 9. “They came at 6am. It was raining and everyone was in the village,” he said. “The women cried out: ‘The Janjaweed are coming’.

“The men and women ran from the village. As they were running, the Janjaweed were shooting.

“The Sudanese military came with five vehicles. They shot the people with machine guns. The Janjaweed threw hand grenades to burn down our houses.”

Mr Abdullahi’s home now is a piece of plastic sheeting spread over a framework of branches, with a handful of possessions inside; blackened cooking pans, a dagger and an ancient plastic tub of blue hair gel. There is a waist-high stockade of branches to keep animals out.

Another refugee, Osman Yahya Khadir, 52, escaped an attack on Gazmoun village last Wednesday. According to his account, Sudanese military helicopters circled in the sky overhead while Janjaweed attacked on the ground.

“When I heard the noise of the helicopters, I ran to hide in the mountains, because I knew the Janjaweed would come,” said Mr Khadir, a tall man in a long, white robe.

“I knew from the other villages that it had happened like that. They told me: ‘When you hear the helicopters and the planes, the Janjaweed are coming’.

“We drove our herds of animals towards the mountains. The Janjaweed came to take our animals and killed five people.” Both these villages have previously been attacked by Janjaweed and government forces, and their inhabitants had fled to Chad.

In recent months, some refugees had returned across the border to rebuild their lives, but renewed attacks have killed or driven away those who went back to Darfur.

Mr Abdullahi, dressed in a khaki green tunic and ragged green trousers, said: “The first time we were attacked was one year ago. Aeroplanes dropped bombs, and there were Janjaweed on horses and soldiers in cars. My father and my father’s brother were killed.

“One month ago, we returned to our village. Everything was destroyed and we rebuilt it all. We only had one or two cows left.

“The government of Sudan sent envoys to Chad to say it is safe to return, and we believed they were telling the truth because they were the state.”

As he speaks, sitting on a straw mat flanked by a group of male refugees, the low growling of an Antonov plane’s engines becomes audible. The men fall silent; the Russian-built planes are the favoured bombers of the Sudanese government.

Many of the refugees are members of the Djabar tribe, which has not played a large part in the Darfur rebellion.

Although there are rebel strongholds to the north and south of the region which has recently come under attack, there is no significant rebel activity in or near these villages.

Instead, the motive for the Janjaweed appears to be an opportunity to acquire the livestock of the black villagers and steal their land.

It is harder to understand why the government continues to back the Janjaweed when there is no rebellion to crush. The refugees believe it is because the regime in Khartoum is racist.

Mr Abdullahi said: “The government of Sudan doesn’t want blacks, they want only Arabs.

“Before the first attack, some Arabs in the region came to tell us: ‘We’re going to send you blacks away and claim this land for ourselves’.”

The landscape of eastern Chad is a mirror image of Darfur. With the rainy season, a transformation has taken place, and a countryside of barren sand, rock and straggling bushes wears a thin covering of green, as if it has been freshly painted.

Herds of camels, goats and cattle are accompanied by wobbly calves, greedily cropping the grass before the dry season returns.

But the refugees say their lands in Darfur were far more fertile than the border region.

Their rival Arab tribes want the land “because the land of Darfur is rich, and there are many animals, plenty of riches, oil under the ground,” said one refugee.

Hundreds of refugees have now fled across the border once again. But even here, they claim, they are being pursued by the Janjaweed.

On August 12, a family of refugees was sleeping in a stockade of branches at Senett when they were fired on. It was then that Hawa Abdullahi was shot through the arm and her brothers, aged 12, 15, 18 and 21, were killed or fatally injured.

Hawa said: “I was sleeping when I heard something in the night. Before I could ask my brothers what it was, there was gunfire. I got up straightaway, then I was hit in the arm and cried out for my mother.”

According to Hawa’s father, Abdullahi Ibrahim, who ran from his sleeping place to the scene of the shooting, the gunman escaped with an accomplice who was holding their horses. They fled in the direction of Sudan.

“This did not happen because they wanted to steal from us,” Mr Ibrahim said. “But because this is the manner in which they treat our people.”

Under a burning sun, Mr Ibrahim, a barefoot man in a tattered green robe, goes to pray over three mounds of sandy yellow earth covered in branches. Three of his sons lie there, while a fourth lies dead at a clinic in nearby Birak.

Fresh green shoots of grass have sprung from the base of each mound, though they are only a week old.

This should be a time of rejoicing and renewal for the black farmers of Darfur; when the long-awaited rains bring the promise of new life. But this year the rainy season is only bringing more death.

Sudan appeared yesterday to have bowed to international pressure over Darfur as the UN announced an agreed plan to tackle the refugee crisis and avert sanctions.

The UN special envoy to the country, Jan Pronk, said the Sudanese government had halted military action against villages in Darfur and lifted restrictions on humanitarian assistance.

Last Friday, the UN security council gave Sudan 30 days to disarm the Janjaweed, the Arab militias deployed by the government to suppress a revolt in Darfur.

Tens of thousands of demonstrators chanting anti-American slogans marched on the UN headquarters in Khartoum yesterday to protest against western troops being sent in to deal with the crisis in Darfur.

The government-sponsored rally took place as the African Union said it would increase troop deployment in Darfur from 300 to 2,000.

The Sudanese government has raised fears of a western intervention in Darfur, although no western country has pledged to send troops.

More than 100,000 protesters gathered in central Khartoum and shouted slogans attacking America and the UN, which has given Sudan 30 days to disarm the Janjaweed, the predominantly Arab militias whose murder, rape and arson has driven more than a million people from their homes. The Sudanese government has used the militias to help suppress a rebellion.