MILAN - Dozens of hooded anarchists clashed Saturday with riot police who blocked their approach to the Austrian border during a protest against plans to tighten border controls to prevent the passage of migrants.

Riot police just 100 to 200 metres (yards) from Italy's border with Austria responded with tear gas after a group of 50 to 80 anarchists who covered their faces with motorcycle helmets and gas masks threw objects including bricks and firecrackers at a police blockade. The news agency ANSA said about 20 protesters were detained and four officers were injured.

Hundreds of Austrian police were deployed, but never activated, on the other side of the border, while helicopters hovered overhead.

The protest spilled over on to the railway, temporarily blocking service, and then onto the heavily travelled Brenner highway, which also suffered delays. As police pushed the protesters deeper back into Italian territory, many shed their helmets and gas masks, scampering up onto a steep hillside overlooking the highway and shouting at police to free their detained comrades.

Italian RAI state television cameras showed police detaining one demonstrator at the railway station, which demonstrators also vandalized, and then another dozen detained in a road nearby. Italian Carabinieri police in Bolzano and Brenner were unable to confirm the number of arrests or injuries.

The demonstration, which included peaceful protesters behind a rainbow flag, comes after Austria announced moves to tighten border controls out of concern that the flow of migrants to northern Europe will shift to Italy after the closure of the Balkans route.

Earlier Saturday, Austria's interior minister, Wolfgang Sobotka, said in nearby Merano that the controls would not be stringent as long as Italy registers all incoming migrants and prevents a large migrant numbers from reaching the border. Austria has appeared to back down on plans to build a wall at the Brenner Pass, saying it would only be put up only in the face of a migrant influx.

The Brenner Pass is an important conduit for tourists and goods transiting Europe, with some 2 million vehicles passing each year.

Italian Interior Minister Angelino Alfano welcomed Sobotka's assurances. Alfano was visiting Ventimiglia, near the border with France, where he said a centre for migrants should be closed to discourage new arrivals.

"Migrants need to resign themselves to the fact that they cannot enter France from Ventimiglia, because we do not want to feed false expectations and because transiting across the Italian border, toward bordering European countries, can be a pretext for building walls," Alfano told a news conference.

News from © The Associated Press, 2016