U.S. agriculture officials said Friday the discovery of genetically engineered wheat in an Oregon field appears to be an isolated incident.

The plants, modified to be resistant to Monsanto herbicide, were discovered last month and led some Asian importers to halt or suspend trade with US wheat growers while an investigation was launched.

Some crops of corn and soybeans are genetically engineered to be resistant to herbicides on the global market, but such modifications to wheat have never been approved anywhere in the world.

"As of today, USDA has not found nor been informed of anything that would indicate that this incident amounts to more than a single isolated incident in a single field on a single farm," said a statement from the US Department of Agriculture.

"All information collected so far shows no indication of the presence of GE (genetically engineered) wheat in commerce."

The USDA said the discovery does not pose any concern to public health or food safety, and recalled that the US Food and Drug Administration completed its consultation process with Monsanto in 2004.

"Completion of the FDA consultation process means this variety is as safe as non-GE wheat currently on the market," it said.

The probe so far has included interviews with the farmer and the seed supplier, USDA said. Samples of the wheat seed the farmer bought, along with sample of his harvests and this year and last have tested negative for GE material.

"Investigators are continuing to conduct interviews with approximately 200 area growers," said the statement.

US officials have also provided trading partners with a DNA-based method for detecting Monsanto modified grain at a frequency of one in 200 kernels, it said.

"Major markets, such as Japan, Korea and Taiwan, have postponed imports of US white wheat as they continue to study information from US officials to determine what, if any, future action may be required," said the statement.

"USDA officials will continue to provide information as quickly as possible as the investigation continues -- with a top priority on giving our trading partners the tools they need to ensure science-based trade decisions."

[Image via Agence France-Presse]