Berlin - A man arrested after walking through town swinging the severed head of his sister-in-law by the hair told police she had provoked him, German prosecutors said on Wednesday.

The 24-year-old man admitted stabbing the woman to death and cutting off her head with a 12-inch kitchen knife after a row, a spokesman at the prosecutors' office in the western city of Aachen said. "The man said he had been provoked before the deed," the spokesman said, but gave no details.

Shocked passers-by had alerted police after seeing the wild-eyed man, carrying the head in one hand and a blood-stained knife in the other, walking through the streets of Uebach-Palenberg, a small town near Aachen.

One witness told the newspaper Bild: "He kept swinging the head by the hair, holding it up like a trophy and showing it to people. His eyes were wide open as though he was on drugs."

Police found his sister-in-law's headless body in his flat.

The prosecutors' office said police were investigating the man's mental state at the time of the attack.

Bild reported that the man was having an affair with his sister-in-law but she wanted to end it.