Eritrean refugees kidnapped in Sudan are raped, beaten, chained and sometimes killed after being forcibly transported to Egypt's Sinai peninsula and held for ransom, Amnesty International said on Wednesday.
The London-based watchdog said it has received "numerous reports" since 2011 that residents of the Shagarab refugee camp in eastern Sudan near the Eritrean border have been abducted.
"Most of those kidnapped have been forcibly taken out of Sudan over the border into Egypt, in most cases to the Sinai region. The majority of the victims report that they are sold between different criminal groups along the route," it said.
In Sinai they are held prisoner while ransom payments are extorted from their relatives.
"According to testimonies and information received by Amnesty International, during their captivity they are subjected to acts of extreme violence and brutality, including rape of men and women and other forms of sexual violence," the watchdog said.
"Some of those who are unable to pay a ransom are killed. Some die as a result of ill-treatment or the terrible conditions of their captivity."
Amnesty quoted one Eritrean who survived eight months in Sinai after his kidnapping from Shagarab early last year.
He described the fate of an Ethiopian victim who said he could not pay, was sexually abused, beaten and set alight.
"After he died, they left his body in the room with us until it became rotten and worms started crawling. They forced all of us in turns to hold him," the Eritrean said.
Amnesty's report comes after the United Nations refugee agency, UNHCR, said in January it was seeing "rising incidents of abductions and disappearances of mainly Eritrean refugees, allegedly involving border tribes," in and around refugee camps in eastern Sudan.
UNHCR spokeswoman Melissa Fleming said that while some refugees are believed to pay smugglers to transport them elsewhere, others are abducted.
"Those who are kidnapped are often held for ransom or trafficked onwards for the purpose or forced marriage, sexual exploitation or bonded labour," Fleming said at the time.
Amnesty expressed alarm at "apparently inadequate safety and security" at the Shagarab camps.
But Fleming said UNHCR is working with other agencies to reduce the risk of abductions.
"The government of Sudan has already deployed additional police and we are supporting the authorities to improve overall security," she said.
Chiara Cardoletti, UNHCR's assistant representative for protection, said 35 people have been identified as victims of trafficking since January, though not all may have been kidnapped.
"We are noticing a decrease in the numbers that we were seeing before, and that is because the government has taken action," she told AFP.
The number of asylum seekers reaching the camp is also down, she said.