A team of Belgian scientists found alien gene fragments in soybeans grown from seed developed by the American biotechnology giant Monsanto Co., which are spliced with a bacterium to make them resistant to the company's Roundup Ready herbicide, Reuters reports.
The discovery comes nearly a year after an unapproved gene-altered corn entered the US food chain, sparking recalls of items such as taco shells from grocery shelves and causing a slump in exports of American corn to Japan.
Marc De Loose from Belgium's Centre for Agricultural Research said he and his colleagues found that the unidentified gene fragments in Roundup Ready soybeans had no link to the plant's DNA sequence or the genome of the soybeans.
However, he added there was no evidence to suggest that the alien fragments could lead to any unknown effects, such as possible allergic reactions in people.
"There is no scientific data to support this idea because we checked this sequence in different generations that were on the market and we didn't see any differences.
This means that the sequence is stable and all the data concerning safety are still valid in my opinion," De Loose told Reuters.
Environmental group Greenpeace said the discovery showed that Monsanto did not know "with any certainty what it is creating through genetic engineering."
A spokeswoman for the US Food and Drug Administration, commenting on the Belgian group's research, said the agency was "aware of it and is looking into it."
Monsanto spokesman Bryan Hurley said: "This is not a (food) safety issue.
The information about the soybeans were characterised by Monsanto more than a year ago and we have shared that with regulatory authorities throughout the world."
According to Hurley, the unidentified gene fragments could be the result of DNA being "rearranged" as a result of the process when the bacterium to make the plants resistant to Roundup Ready soybeans was inserted.
Hurley said he did not foresee any loss of consumer confidence in foods produced from gene-altered crops.
Chairman of the American Soybean Association, Tony Anderson, said: "Unless there is something definitive, to me, that there is a problem, I am still of the belief that we have a product that is safe and allows us to be more efficient with our farming practices.
We believe in good sound science.
"And if the day should come that good sound science says we need to rethink this, then we will rethink it.
But if the good sound science tells us over and over we got a product that is safe, let's stay with it," he added.