The US government said Monday it was investigating a type of genetically-modified (GM) corn, approved for use in livestock, that may have turned up in some taco shell's at the popular fast-food chain Taco Bell.

There is some concern that a protein found in the altered corn could cause an allergic reaction in some consumers, which is why the FDA had not approved of its use in humans.

The US government is currently in the process of finalizing guidelines for the approval of new varieties of GM foods.

US government scientists claim that the GM corn, named "StarLink", is safe for cattle, pigs and other farm animals.

Regulators said if they determined the corn was in the taco shells, the products would be immediately pulled off the market. "If we find there was any infraction, then we're going to come down very, very hard on those responsible," said Dave Cohen, a spokesman for the Environmental Protection Agency (EPA). The EPA and the Food and Drug Administration (FDA), share authority over gene-spliced foods, and are jointly investigating the accusations.

The presence of the unapproved corn in Taco Bell shells sold in grocery stores, is being alleged by the anti-biotech organization Friends of the Earth (http://www.foe.org/), who also have an exclusive anti-GM activist page at http://www.gefoodalert.org.

The boxes of taco shells sold under the Taco Bell brand were produced by Kraft Foods Inc., a unit of Philip Morris Co. Inc.

The corn variety in question (StarLink) was developed by Aventis SA and is another type of Bt corn, which is spliced with a naturally occurring plant pesticide known as bacillus thuringiensis, which is deadly for the European corn borer.

According to Friends of the Earth, independent laboratory, Genetic ID Inc., concluded in three sets of tests that the samples contained StarLink corn.

Samples of taco shells from Taco Bell restaurants will also be tested soon, group members said.

The testing was done by Genetic ID Inc. at the request of Friends of the Earth. Three sets of tests, performed first in August, all found evidence of the Cry9C protein in the taco shells, said Jeffrey Smith, vice president of Genetic ID.

No illnesses have been reported from the taco shells, in part because consumers are unaware the product contains a potential allergen, the group said.

"This raises disturbing questions about the adequacy of the US regulatory system for genetically modified foods," said Jane Rissler of The Union of Concerned Scientists (http://www.ucsusa.org/), a member of the anti-biotech coalition. "The FDA has yet to require a single test for safety."

Kraft Foods said it was trying to locate and test the same batch of taco shells analyzed by Friends of the Earth. Nearly 150,000 boxes of Taco Bell shells, each containing a dozen, were produced in the same batches as those supposedly contaminated.