WASHINGTON (Reuters) - More than one dozen cases of liver failure and death were reported in patients taking GlaxoSmithKline Plc’s Avandia, advocacy group Public Citizen said on Thursday in a petition calling for a ban of the diabetes drug.

But GlaxoSmithKline defended its drug, saying its own review by an independent panel earlier this year said the liver risks were acceptable.

“We do not believe there is a connection between liver toxicity and this medicine,” the company said in a statement, adding it had not yet read the group’s petition.

Public Citizen said its review of U.S. Food and Drug Administration data found 14 previously unpublished cases of severe drug-induced liver failure, including 12 deaths.

That risk, coupled with other known complications that include heart failure, fractures and vision loss, was too great to allow the drug to continue to be sold in the United States, especially with other treatments available, it said in a petition to the FDA.

“The evidence for this unique combination of toxicities is compounded by the accompanying lack of evidence of any clinical benefit, compared to other approved drugs for diabetes,” the petition said.

Sales of Avandia -- also known as rosiglitazone and part of a new class of drugs to treat type 2 diabetes called glitazones -- have plunged in the past year after the heart risk surfaced in an analysis of available clinical studies.

Since then, experts at two major diabetes associations have withdrawn their support of the drug, instead backing lifestyle changes such as diet and exercise as well as other treatments.

Still, Public Citizen estimated about 10,000 prescriptions continue to be filled each day. “Thus, it is urgent for the FDA to immediately ban rosiglitazone,” it said.

Representatives for the FDA did not immediately return requests for comment.

The British drugmaker’s shares trimmed earlier gains and were off 94 cents, or 2.5 percent, at $36.37 in morning trading on the New York Stock Exchange. In London, its shares were down more than 2 percent.