Six illegal miners have been shot dead in the Democratic Republic of Congo's main diamond mine, Miba, near the central town of Mbuji-Mayi.
Illegal mining is widespread in Mbuji-Mayi
The diamond workers' union blamed the deaths last week on armed guards who work at the mine, known as "suicidals".
A BBC correspondent in DR Congo says illegal miners are often killed when pits fall in on them.
The Miba mine produces diamonds worth $6m-8m every month and attracts up to 10,000 illegal miners a day.
Sources in Mbuji-Mayi told the BBC's Arnaud Zajtman that the shoot-out happened at night between two groups of "suicidals" who were fighting over a diamond-rich deposit.
But union official Jean Marie Kabuya Mulamba said those killed were unarmed miners.
Every week an average of four or five miners are killed.
But the miners' union said this latest incident is the most deadly in recent months.
Miba manager Gustave Luabeya said that 300 armed policemen and 1,000 unarmed private guards are not enough to prevent the clandestine miners from accessing the mine.
But he insisted that none of the guards had been involved in the incident.
Clandestine miners live on less than $1 a day.
Local inhabitants say the mine does not bring any profit to the local area.