GENEVA — An 8-year-old girl was among those injured by letters containing acid that were sent to the families of Geneva bank executives in recent days, the magistrate investigating the case said Thursday.

The girl was taken by ambulance to a hospital after she opened a box inside one of the letters and her hands were burned by concentrated sulfuric acid, Michel Graber, the magistrate, said by telephone from Geneva.

Two adults were also injured, but apparently less seriously, by the letters, which targeted Geneva private bankers and their families, he said.

Mr. Graber said that a total of eight letters containing acid were mailed to eight different addresses, in several cases the wives of executives at Geneva private banks. The letters were mailed from within Switzerland, but were routed through a central post office so it was not possible to say from where. The letters were sent Sunday, the Swiss newspaper Tribune de Geneve reported.