Pete Doherty was fined $1,900 after police found traces of cocaine in his blood following a performance by his rock band at the Hultsfred music festival in Sweden.

Police detained the 27-year-old Babyshambles frontman after the concert because "he showed signs of being under the influence of narcotics," Ulf Karlsson, a police spokesperson in the city of Kalmar on Sweden's southeastern coast, said Saturday.

Tests showed traces of cocaine and the tranquilizer benzodiazepine, Karlsson said. He said Doherty had a prescription for the tranquilizer. Doherty was fined and released, Karlsson said. He said Doherty was not in possession of any illegal drugs, so he will not face other charges.

Bands: Libertines