Thirteen police officers were injured overnight in clashes with protesters against a new high-speel rail line between France and Italy in the northern town of Chianocco, officials said on Thursday.
Protesters threw rocks and police fired tear gas after security forces moved in to clear a section of motorway blocked for three days by protests against the building of the rail line through a picturesque section of the Alps.
Organisers said some activists were also injured but did not say how many. Four protesters were detained although three of them were later released.
Protest organisers are calling for fresh protests later on Thursday.
Interior Minister Anna Maria Cancellieri called for dialogue but said she would enforce "absolute discipline" against violent protests.
The rail line, which will connect Lyon and Turin, will cost 20 billion euros ($26.7 billion,Dh98.07bn) and is strongly opposed by some local residents in the Val di Susa in the Alps -- who say it is costly and bad for the environment.
Its supporters say it is a vital project for Europe and would shorten the journey between Paris and Milan to four hours instead of seven hours at the moment, as well as taking a lot of truck traffic off the motorways.
The project is expected to be completed by 2023.