A grisly scene was discovered in Tripoli today, when reporters came across a former Gadhafi camp in central Tripoli where pro-regime fighters were found massacred, including a number that were bound before their execution.

In a discovery the UN termed “alarming,” a number of the victims were also found in the field hospital, having been executed there while receiving treatment for wounds. Reports have the death toll in this single incident at over 30.

UN spokesman Rupert Colville promised an investigation into the killings, and urged rebel leaders to “take active steps to ensure that no crimes, or acts of revenge, are committed.” One rebel ambassador insisted the leadership had already ordered fighters “not to kill anybody” and that it couldn’t possibly have been the rebels who massacred the Gadhafi troops.

Yet the growing concern about the behavior of the rebels hardly begins or ends with this single incident. Amnesty International is also reporting that the rebel faction has been conducting mass arrests of black people across the nation, terming all of them “foreign mercenaries” but with growing evidence that a large number were simply migrant workers.

In rebel custody, the migrant workers are subjected to routine beatings and, according to testimony from one of them, they are told by rebel guards that they will be “eliminated or else sentenced to death.”