Several people were slightly injured in scuffles with a line of police who fired teargas, though security forces did not act to stop protesters entering the site at Venaus, some 60 kilometres (37 miles) from Turin.

The protesters had been ousted from the site on Tuesday in a police charge which injured around 20 people.

The government had deployed 1,000 riot police to prevent the protesters occupying the site Thursday, but political allies of Prime Minister Silvio Berlusconi did not agree on whether they should intervene again.

Employment Minister Roberto Maroni, a member of the locally popular Northern League, spoke out against police action on Thursday and called for dialogue to solve the crisis.

A 53-kilometre (33-mile) cross-border train tunnel into France is due to be cut through the valley, arousing the anger of people living in the region who question the usefulness, cost and environmental consequences of the project.

Thursday's marchers numbered nearly 40,000, according to one participant, Gianandrea Torasso, a local mayor.

Earlier this week opponents of the project blocked roads into the area and announced a national demonstration in Turin on December 17.

Italian Prime Minister Silvio Berlusconi has denounced what he called "the activism of extremist left-wing groups and anarchists", and promised to respond with total firmness.

Turin is to host the Winter Olympics in February 2006 and a massive security operation is already being planned.

The Turin-Lyon link, considered a key element of a planned network of high-speed railways across Europe, will cost an estimated 12.5 billion euros (15 billion dollars) and is set to be completed by 2020.

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