Shagarab Refugee Camp, SUDAN — Moving at night through the cold, flat desert, armed people smugglers are exploiting, abducting and sometimes killing Eritreans fleeing their authoritarian homeland, the UN and refugees say.

"People catch us, sell us like a goat," one Eritrean asylum-seeker said of the human traffickers.

Like others who have reached this wind-blown collection of shelters inside the Sudanese border, he accused the local Rashaida tribe of involvement in the people trade, which the United Nations refugee agency (UNHCR) is hoping to counter through a $2-million effort to support local police and improve camp security.

"These groups that are involved in this are heavily armed. We hear of firefights between government forces and these armed groups," said Felix Ross, the UNHCR's senior protection officer in Sudan's eastern region.

He told AFP the problem has emerged over the past two or three years, with the UNHCR hearing of at least 20 kidnapping cases a month.

"But we believe that the number itself is much higher," Ross said.

On a visit to the Shagarab camp on Thursday, the UN High Commissioner for Refugees, Antonio Guterres, said a global criminal network of smugglers and kidnappers is "taking profit of the desperate situation of many Eritreans."

Shagarab camp receives about 2,000 asylum-seekers monthly, largely from neighbouring Eritrea where many have fled compulsory military service.

The UN estimates that 80 per cent of the new arrivals leave the camp within two months for Khartoum, Egypt, Israel or further afield, in search of better economic opportunities.

"Due to the limitation on the freedom of movement of refugees in Sudan, refugees and asylum-seekers resort to smugglers to transport them into, through and out of Sudan," a UNHCR briefing paper said.

But some simply end up being kidnapped for ransoms which the UNHCR said can reach $10,000.

"Here there is not security. There is many person kidnapped," an Eritrean who has spent four months at Shagarab said, speaking in English.

He and other Eritreans interviewed during a UN-organized visit cannot be named, for their own protection.

One 23-year-old woman — who like the men said she had fled military service — said smugglers took her in 2010 from Eritrea to Egypt, "and when we arrived there they asked my family for more money," which they did not have.

She was arrested and jailed before being deported and then making her way — this time without involving traffickers — to the Sudanese camp.

An Eritrean man, aged 27, said camp residents face a risk of being snatched if they walk out to the toilet area at night.

Others are "kidnapped by Rashaida" on their way in from the border, he said at the one-room cement block he shares with 25 other men. Their belongings hang from the wall beside a picture of Christ.

"They ask them for ransom money . . . some of the people said it's about 50,000 pounds ($12,000)," he said through a translator. "Most of the time they cannot pay, so they are tortured."

UNHCR chief Guterres said some refugees who ended up in Egypt's Sinai peninsula were "killed for the traffic of organs."

The Rashaida are a camel-raising tribe whose buildings near the state capital Kassala are painted bright pastel pink and blue.

The area around their roadside market, a row of corrugated metal shacks, is believed to be a smuggling hotbed for everything including people, Ross said.

Human traffickers are "making a lot of money in a region where it's difficult to earn money," he said.

"We know that in the refugee community there are people working with these criminal groups."

Between Kassala and the camps 120 kilometres away, the Eritrean border lies beyond trees barely visible in the distance across the barren brown earth — the smugglers' turf.

"If you were to travel here by night you would see a lot of lights crossing through the desert," Ross said.

Sudan's refugee commission recognizes almost all of the new asylum-seekers as refugees, but if they stay in the camps they could wait years for resettlement, and have little in common with older refugees or the local population.

The Eritreans arriving since 2005 are mostly Christian and not Arabic speakers, in contrast with an older group of mostly Muslim Eritreans who began fleeing to Muslim-majority Sudan four decades ago during their country's independence war with Ethiopia, the UN says.

"How about us, the newcomers?" an Eritrean who has spent eight months at the camp asked AFP. "Nobody cares about us."