Several Austrian supermarkets are pulling some brands of bitter chocolate off their shelves after a consumer group found traces of mineral oil in samples.

Austria's Consumer Information Organization, which carried out the tests, says a third of 20 products examined had traces of mineral oil, and that these contained minute amounts of carcinogenic substances.

State broadcaster ORF said Monday that discounters Lidl and Hofer have removed their own brands, and at least one local producer has recalled its product. Others whose chocolate also contained the traces have not followed suit, however. They say there are no guidelines on how much of the substance is harmful to human health.

Consumer protection groups say the oil could have originated from machines used for production or from the packages used for cocoa beans.