Prosecutors have launched proceedings against a Brazilian woman who claims to have miscarried twins after an alleged attack last week by neo-Nazis in Zurich.

The Zurich prosecutor's office said on Wednesday the 26-year-old lawyer was suspected of misleading law-enforcement authorities. Her passport and legal papers have been blocked.

Police said the woman claimed she was attacked outside a Zurich train station by three skinheads, one with a Nazi symbol tattooed on the back of his head, and that the purported assailants cut the initials of the rightwing Swiss People's Party into her stomach and legs, causing her to miscarry twins.

Pictures of her scarred body appeared in newspapers and Brazil's foreign ministry raised the possibility that she was the victim of a xenophobic attack.

But after a series of tests police said the woman was not three months pregnant as she claimed, and a forensic specialist from Zurich University called it a "textbook case" of self-mutilation.

All of the wounds were in areas reachable by hand and none was severe or on particularly sensitive areas, according to experts.

Prosecutors want to keep the woman in Switzerland to ensure her presence during the criminal investigation. She was provided a defence lawyer on Tuesday.

The prosecutors will also continue to investigate her claims of an attack, they said.

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