Karl May, the author to whom the museum is dedicated, wrote the bestselling Winnetou novels. Photograph: Martin Foerster/dpa/Corbis

He is the man who started a long-running German fascination with the Wild West. But now a museum dedicated to the adventure novelist Karl May is accused of disrespecting the wishes of the tribes that once inspired his stories by refusing to hand over a collection of native American scalps.

Since its foundation in 1928, the Karl May Museum in Radebeul near Dresden has been in possession of 17 scalps that were bequeathed to the private collection by a friend of the novelist. Three of the artefacts are currently on display.

For the last four years, US activists have been calling for the return of the scalps, whose display in American museums has been illegal since 1990. Yet in spite of an official letter from an umbrella group representing North American tribes requesting the return of the artefacts having been handed to the Karl May Museum last month, the museum has made no moves to return the items.

Contrary to popular belief, scalping was not practised solely by native Americans, but also widespread among European colonists – one of the authors who has helped to popularise the conception of scalping as a native American tradition was Karl May himself. The author of the bestselling Winnetou novels didn't visit America until after his literary success, but frequently projected the idea that his books were autobiographical.

The majority of scalps in the Radebeul collection were handed to the museum by a friend and admirer of Karl May's, a circus artist named Ernst Tobis, who went under the stage name "Patty Frank". According to his biographer, Tobis purchased his first scalp, originally belonging to a chief of the Ojibwa tribe, in return for two bottles of whiskey, a bottle of apricot brandy and 1,100 US dollars, during a trip to a native American reservation in 1904.

A spokesperson for the descendants of the Ojibwa tribe told The Guardian that displaying the scalps in a museum was "inappropriate and unacceptable". "These are human remains which should be buried respectfully and should never have been taken from the tribe in the first place," said Cecil Pavlat, a repatriation specialist working for the tribe, now more commonly known as the Sault Ste. Marie Tribe of Chippewa Indians.

Yet Hans Grunert, the exhibition curator at the Karl May museum said that the exhibits were "part of history", and that "it is important to the museum that history isn't being falsified in our exhibition". He conceded that the museum was "prepared to have a conversation" with descendants.

Members of the Chippewa tribe say they are considering staging a protest at a festival celebrating Karl May's legacy in Radebeul in May.