The authorities in six German states have ordered retailers to stop selling Red Bull Cola energy drinks after traces of cocaine were found in it.

The recall came after a sample analysis conducted in North-Rhine Westphalia found one litre of the drink contained 0.4 micrograms of the banned substance. Officials said the cocaine levels were too low to pose a health threat but were not permitted in foodstuffs.

Red Bull said its cola was "harmless and marketable" in both the United States and European Union. The company said coca leaf extracts were used worldwide as a natural flavoring, and that its own tests had found no traces of cocaine.

The illegal cocaine alkaloid - one of 10 found in coca and representing only 0.8% of the plant's chemical make-up - is chemically removed before use, as mandated by international anti-narcotics agencies.

"There is no scientific basis for this ban on Red Bull Cola because the levels of cocaine found are so small," Fritz Soergel, the head of the Institute for Biomedical and Pharmaceutical Research in Nuremberg, Bavaria, said.

"And it's not even cocaine itself. According to the tests we carried out, it's a non-active degradation product with no effect on the body. If you start examining lots of other drinks and food so carefully, you'd find a lot of surprising things."