A spokeswoman said she could confirm reports about the existence of the sweetener, but was unable to give further details.
According to reports in the Wall Street Journal, Coca-Cola has filed 24 patent applications for the product, which has been tentatively named Rebiana.
It plans to use the sweetener in some of its beverages.
It is believed that Cargill may also use the sweetener in some of its food products.
Stevia is only approved in the United States as a dietary supplement, not as a food additive.
Therefore the first markets for the new sweetener could be outside the US.
The authorities in 12 countries have approved Stevia as a food additive, including Japan, Brazil and China.
However, Cargill is thought to be working on clinical trials of the sweetener and planning to use the results to petition the Food and Drug Adminstration (FDA) for permission to use rebiana as a food additive in the US.
Stevia is a member of the daisy family, and the extract is claimed by Steviainfo.com to be "the world's only all-natural sweetener with zero calories, zero carbohydrates and a zero glycemic index".
Extracts are said to have up to 300 times the sweetness of sugar.
As a sweetener, stevia's taste has a slower onset and longer duration than that of sugar, although some of its extracts may have a bitter or liquorice-like aftertaste at high concentrations.
Most non-diet soft drinks in the United States are currently sweetened with high-fructose corn syrup, which has come under increasing criticism for contributing to obesity.
Lower-calorie sodas are made with artificial sweeteners such as saccharin, aspartame and sucralose.
UK newspaper The Times has speculated that the development could be an indication that Tate & Lyle's sucralose is falling out of favour.
In its full year 2007 results, released last month, Tate & Lyle said that its Splenda sucralose brand had achieved only modest growth, which was disappointing.
A recent report by Freedonia revealed that the US sweetener market is poised to increase 4 percent per year, to reach over $1bn in 2010.
A company that could offer a natural alternative to artificial sweeteners may have found the winning ticket to reaping the rewards of this growing market.