At least three reinforced tunnels were discovered earlier this month under Paris's only prison complex, prompting an inquiry as to their origin and purpose, a judicial source told AFP on Wednesday.
Authorities were alerted to the existence of the tunnels by inmates who heard noises underground at night, the source said.
The recently dug tunnels run horizontally several meters underneath the Prison de la Sante, an aging complex located in southern Paris' 14th arrondissement that has been nicknamed "the sieve" due to frequent escapes.
It is not clear, however, whether the crudely reinforced tunnels - which do not communicate at any point with the prison - were linked to any planned or attempted escape, the source said. Two of the tunnels pass underneath guard towers, and the third under the main entrance of the prison.