Two officials for a Dutch firm accused of sending toxic waste to Ivory Coast are reported to have been attacked in jail in Abidjan, say company officials.
Residents suffered headaches, vomiting and breathing difficulties
Trafigura has called for the immediate release of its executives, Claude Dauphin and Jean-Pierre Valentini, who were arrested two months ago.
The men are unhurt but it is the third reported attack, the firm says.
The company denies responsibility for the waste, which left 10 people dead and thousands in hospital.
The firm also says it has started libel proceedings against UK firm Leigh Day & Co, which is suing Trafigura for £100m ($191m) on behalf of Ivorian victims at a court case filed in the UK.
Dutch lawyer Bob van der Goen also says he is suing Trafigura in a Dutch court.
Trafigura says the publicity over the case is exacerbating the situation of its detained executives.
The firm says it has received reports that gangs "of up to 100 young prisoners" were able to arm themselves with knives and kitchen tools and attack a small number of men, including Mr Dauphin and Mr Valentini.
It says that an Ivorian accused of complicity in the scandal suffered serious knife wounds before order was restored.
Last week, the Ivorian authorities said they had carried out a cull of some 450 pigs which had eaten the toxic waste, which was dumped at sites across the main city, Abidjan.
The waste is being sent to France for disposal
Some 3,000 metric tons of waste - of which 528 tons was waste originating from the Probo Koala - has now been sent to France for disposal. More shipments are expected.
Trafigura first attempted to discharge the chemical slops from one of its tankers, the Probo Koala in the Dutch port of Amsterdam in early August.
But the company that was to dispose of the waste suddenly increased its charges dramatically - asking for 40 times more to treat the waste.
Trafigura refused, and the tanker proceeded to Nigeria.
There it failed to reach an agreement with two local firms about offloading the waste and only in Ivory Coast did it find a company to handle the waste.
On 19 August the waste was discharged near Abidjan. Two weeks later the first complaints arose.
Instead of being incinerated as it should have been, the waste had been dumped.
Once people began dying, Mr Dauphin and Mr Valentini travelled to Abidjan to offer their help.
They were arrested on 18 September - four days after their arrival and have been held in Abidjan's Maca prison since.