* Government says has no plans to scrap rail project
* Protest most serious to face PM Mario Monti's government (Adds clashes in Milan, details)
By Elisa Sola
VAL DI SUSA, Italy, March 1 (Reuters) - Demonstrators opposed to a high-speed train line linking Italy to France blocked roads, motorways and railway stations in several Italian cities on Thursday, escalating a long-running protest that has turned increasingly violent.
A group of about 1,000 protesters occupied a portion of a highway in the Val di Susa, an Alpine valley near Turin where work on the project is due to take place, setting up roadblocks and fires using tyres and pieces of metal.
Others briefly blocked tracks at the city's main station, preventing trains from departing. There were similar demonstrations in Bologna, Genoa, Trieste, Palermo.
In Milan, scuffles broke out between police in riot gear and hundreds of demonstrators at the Centrale railway station.
In Rome, around 100 protesters set fire to rubbish bins and stormed the offices of the centre-left Democratic Party (PD) which has distanced itself from the demonstrations.
Thursday's protests followed a night of clashes between hooded, stone-throwing demonstrators and police, who used water cannons and teargas to disperse the crowd.
Police said 29 policemen were injured in the clashes, while the demonstrators said around 100 of their own had been hurt in the most serious protest facing Prime Minister Mario Monti's technocrat government since it took office in November.
"What we saw overnight was really urban warfare," Sandro Plano, who represents 23 Val di Susa mayors opposed to the train link, told Reuters.
"They will not be able to resolve this issue with batons and teargas. The government must listen to the people," he said.
The government said it would go ahead with plans to build the train line despite the protests and Monti said he would meet top ministers on Friday to assess security issues connected to the plan.
"The government, the Piedmont region and the city of Turin confirm their commitment," the Interior Ministry said in a statement, calling the high-speed train "essential."
Villagers in Val di Susa have held repeated demonstrations against the planned train link, a 15-billion-euro ($20 bln) project signed off by Italy and France in 2001 which is supported by the government and backed by European Union funds.
Critics say it will damage the environment, spoil the picturesque landscape and waste public money that would be best put to use to solve the economic crisis.
Opposition has spread beyond the local area, winning support from a wide range of groups.
Protesters say they will not back down until the project is scrapped, but Interior Minister Annamaria Cancellieri said in a newspaper interview on Thursday that stopping the construction work was not an option. ($1 = 0.7501 euros) (Reporting By Elisa Sola; writing by Silvia Aloisi; Editing by Sophie Hares)