Tens of thousands of demonstrators protesting against the railway occupied the site of the planned Alpine tunnel in Italy's northwestern Susa Valley.

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

About the same time as the protest was under way, Berlusconi voiced his determination at a press conference in the capital, Rome, to see the multi-billion-euro project come to fruition.

"The high-speed rail link is a job which it is impossible to give up on, and all the guarantees have been taken on the aspect of the environment," he told reporters.

The protesters were dislodged from the site on Tuesday in a police charge that injured about 20 people.

The government deployed 1,000 riot police to prevent the protestors occupying the site on Thursday, but Berlusconi's political allies were divided 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 to be cut through the valley, angering people living in the region who question the usefulness, cost and environmental consequences of the project.

While valley communities are sharply opposed, the proposed rail link is backed by both governments, the European Commission and the region of Piedmont.

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.

The Italian prime minister denounced what he called "the activism of extremist left-wing groups and anarchists" and promised to take action, although he also acknowledged there had been communication failures.

"You only have to think of the pollution caused by heavy goods vehicles to realise the interest of this rail link and to not call into question such a project," Berlusconi said.

Opponents denounce both the inconvenience and dangers of the project, especially for the water basin during tunneling into the mountain side because of the presence of uranium and asbestos.

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 due to be completed by 2020.

Six thousand trucks pass through the Susa Valley every day.

Two million trucks cross the Alps frontier between France and Italy every year. Freight traffic is forecast to grow to 80 million tonnes by 2030.

The aim is to increase the share transported by rail from 10 million to 40 million tonnes.

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