The US Department of Agriculture (USDA) says an experimental variety of genetically engineered cottonseed developed by Monsanto may have entered the US food system before being properly approved.
But the USDA says there are no food or feed safety concerns related to this incident at this stage.
Its Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) are working together following notification by the Monsanto that a small amount - less than an acre - of an unauthorized GM cotton variety was harvested along with 54 acres of a commercially available GM cotton variety.
According to Monsanto, an estimated 60 tons of cottonseed was harvested, of which less than 0.5pc was from the unauthorized GM cotton variety.
This unauthorised GM cotton variety produces a pesticide that is a plant-incorporated protectant (PIP) nearly identical to a registered product already in a marketed corn variety.
EPA and FDA have concluded that there are no food or feed safety concerns related to this incident.
Also, if animals had consumed meal made from the unauthorised GM cotton variety, there would be no residues in the meat, milk or eggs, USDA said.
Additionally, USDA has determined that the unauthorized GM cotton poses no plant pest concerns.
The US government is investigating whether a small amount of meal from the unauthorized GM cotton variety may have been inadvertently released into the animal feed supply, although it has not been determined whether unauthorised cottonseed meal actually entered the feed supply.
The processor is holding potentially affected material (both processed and unprocessed) pending further investigation.