PARIS — French prosecutors opened a preliminary investigation Tuesday into accusations that Budget Minister Jerome Cahuzac earlier in his career had a secret Swiss bank account to avoid France’s high taxes.

The announcement that an investigation was being launched, from the Paris prosecutor’s office, was described as an attempt to get to the bottom of the reports from the investigative website Mediapart, and not as an indication that authorities have their own reasons to suspect Cahuzac of tax evasion.