By BBC (email the author)
Former rebels in the Democratic Republic of Congo who now serve in the army are running mafia-style extortion rackets in the mines, campaigners say.
The country has some of the world's richest mines, which provide minerals to the global electronics industry.
Ex-rebels of the CNDP group are said to have gained far greater control of the mines than they did as insurgents.
Campaign group Global Witness says the government and international community have failed to demilitarise the mines.
The ongoing conflict in Eastern Congo, which has claimed some six million lives in a little more than a decade, has long revolved over access to its mineral wealth, not just by DR Congo but also its neighbour Rwanda through its proxy forces.
After last year's high profile government offensive against one rebel group which controlled many of the mines in eastern Congo, the military has moved in and transferred power to a competing armed group.
A move to integrate rebels from the CNDP – whose leader Laurent Nkunda has been under house arrest in Rwanda since last year – into Congo's national army has seen them enjoying more control of the country's mineral wealth than ever before, according to Global Witness investigators.
In one mine in South Kivu, civilian miners claimed they were being forced to pay $10 each to the military for permission to spend a night working in the mines.
Researchers say that instead of protecting civilians, the military is taxing them illegally, and subjecting them to abuse.
They also claim that high profile international companies are still knowingly sourcing minerals from these militarised mines. A number of UN Security council resolutions have called for tougher action against those that purchase minerals that originate from armed groups in the Congo.
But so far the international community has stopped short of imposing sanctions on individual companies, despite mounting evidence that many mines are controlled by the men with guns.