Pepsi-Cola is still using caramel coloring containing a chemical linked to cancer in rodents, a report released on Wednesday showed, more than a year after the beverage maker promised to phase it out.

The Center for Environmental Health said that PepsiCo Inc. lagged its rival Coca-Cola in removing the chemical, called 4-methylimidazole, or 4-MI.

Coke and Pepsi said in March 2012 that they would make changes to the production of the caramel coloring used in their namesake colas to avoid the need to label the packages with a cancer warning following a California ballot initiative aimed at limiting people's exposure to toxic chemicals.

This spring, CEH tested samples of Coke and Pepsi purchased from California and 10 other states. Its findings showed no 4-MI in any soda from California. In the samples from the other states, CEH said nine of 10 Coke drinks had little or none of the chemical, while all the Pepsi samples did.

"Pepsi's delay is inexplicable," Michael Green, CEH's executive director, said in a statement. "We urge the company to take swift action to provide all Americans with the same safer product they're selling in California."

In response, PepsiCo said the modification for the rest of the United States would be completed by February 2014. It said it is also undertaking the effort globally, even though regulators in the United States, Europe and Canada consider the chemical safe.

Very high levels of 4-MI have been linked to cancer in animals. It was added last year to a list of chemicals covered by California's Safe Drinking Water and Toxic Enforcement Act of 1986, also known as Proposition 65.

Coke said it modified its sodas for California first so they would not have to carry a warning. But since it makes no sense to have separate inventories of products, it started using a modified caramel for U.S. markets beyond California.

The U.S. Food and Drug Administration said last year that a person would have to drink "well over a thousand cans of soda a day to reach the doses administered in the studies that have shown links to cancer in rodents."