A Darfur rebel leader says he has become a prisoner at the United Nations peacekeeping base in Kadugli in Sudan.
Two million people have been forced to flee Darfur's conflict
Suleiman Jamous says he cannot leave for fear of being arrested by the Sudanese authorities.
Mr Jamous was airlifted out of Darfur eight months ago for medical treatment after he refused to sign a regional peace agreement.
The airlift prompted criticism from the Sudanese government, which then suspended UN activities for two days.
The BBC's Jonah Fisher in the capital, Khartoum, says that in the murky, confused world of Darfur rebels, Suleiman Jamous is as respected and articulate as they come.
Aged 62, his experience was vital in the early days of the crisis as he co-ordinated humanitarian access for the vast aid operation, he says.
In May last year Mr Jamous rejected the Darfur peace agreement - and was promptly detained by those rebels who did sign.
After a month the UN intervened and flew Mr Jamous to Kadugli for medical treatment.
But our correspondent says the UN seem keen to forget their unwelcome guest, and their clinic is unable to find what is wrong with Mr Jamous's deteriorating condition.
The mission has refused to allow journalists to visit him.
"Because of the background to this problem, we're in sensitive discussions with the government [Sudanese]," the acting head of mission Taye Zerihoun explained.