By Mark Dummett BBC, Kinshasa

A human rights organisation in Kinshasa says its investigators have come across a fresh mass grave in a cemetery near the city limits.

The victims were all executed last week by the Democratic Republic of Congo's military court, according to Voix des Sans Voix, or Voice of the Voiceless,

The authorities have so far denied the report.

Armed robbery

According to Voice of the Voiceless 15 men were executed in secret on the night of 6 January.

The human rights organisation says they had all been condemend to death by Congo's controversial military court for armed robbery and had been serving time in Kinshasa's central prison.

Relatives of the 15 men have been told their sons were transferred

Voice of the Voiceless says none had anything to do with the Laurent Kabila murder trial, in which 30 people were condemned to death last week.

According to the rights investigators the 15 men were led out of the prison hooded and in chains, and were taken to a cemetery in Mikonga, near the capital's Ndjili international airport, where they were then executed.

The investigators spoke to nearby residents and soldiers and later visited the mass grave, where they saw the bodies had been incompetently buried - limbs were still sticking out of the ground, they said.

No right to appeal

Voice of the Voiceless says relatives of the 15 men who have since visited the prison have been told their sons were transferred.

The director of the prison and the chief prosecutor for the military court told me they knew nothing about the executions.

Col Kapend was sentenced to death last week

Human rights minister Ntumba Luaba said he could not confirm the reports, but would lauch an inquiry.

If confirmed, these 15 executions will be the first known to have taken place since a moratorium on the death penalty was lifted last October.

Human rights organisations deplored this decision, and have consistently criticised the military court for its unfairness.

They say prisoners have little chance of a decent trial and no right to appeal.