Congolese diamond miners who have been expelled from Angola say they were subjected to horrifying abuses by security forces.
Angola is expelling thousands of illegal foreign miners
Médecins Sans Frontières (MSF) says people being treated at their centres in Kamonia, southwest DR Congo were tortured and sexually abused.
Head of mission Alain Decoux said they have received similar reports from five diamond mining sites in Angola.
But Finance Minister Jose Pedro de Morais has had denied the allegations.
Some 40,000 Congolese miners have arrived in the provinces of Bandundu and Western Kasai in the Democratic Republic of Congo since 2 April, following a crackdown by Angolan authorities.
An estimated 500,000 Congolese work illegally in diamond mines in northern Angola, the United Nations says. This month's expulsions have been the third and largest wave of forced repatriations since December.
As they are expelled, miners and their families are forced to cross the Tungila river into Congo, where some have drowned, the UN said.
The miners accused Angola's military of sealing off a mine Kaninda (Lunda Norte) for four days - leaving those inside with no food or water.
They told MSF officials that the Angolan military separated families before subjecting them to an intrusive strip-search for money and diamonds.
The Congolese miners allege that they were tortured with fire and machetes and men were forced to perform sexual acts on soldiers while women were raped.
"We have information from people from at least five other diamond mining sites confirming that Kaninda is no exception. What is being allowed to happen is unacceptable," said Mr Decoux.
But Dr de Morais told the BBC the miners were exaggerating and had not been subjected to ill treatment.
"We are not putting these people in five star hotels. They have made lots of money from illegal mining and they are simply changing the story," he told the BBC Focus on Africa programme.
But MSF says many people have spoken of the existence of prisons for miners at Kakanda and Lukapa that are surrounded by anti-personnel mines to prevent escape.
The reports say Congolese civilians are being used as human shields around several of the mines during clashes between Angola's armed forces and the Tigers - ex-gendarmes originating from the Katanga region of DR Congo who run sections of the mines - for control of the valuable resource.