Strasbourg, France  - Groups of anti-NATO protesters skirmished with police in central Strasbourg on Saturday as the leaders of the 28-member alliance prepared to meet for a summit celebrating its 60th anniversary.

Ironically singing "Happy Birthday, NATO" and waving rainbow-coloured banners, the young demonstrators were met by teargas canisters fired by groups of police officers in riot gear.

Some 10,000 police officers and gendarmes were deployed in and around the city, whose downtown districts were otherwise as deserted as a ghost town.

Police said 25 people were arrested overnight as several hundred protesters, many of them carrying iron bars and rocks, tried to sneak into the centre of the city.

By mid-morning some 1,800 protesters had infiltrated the city, provoking police and blocking tramway and bus routes. But they failed in their primary goal of blocking the motorcades carrying NATO leaders.

The daily Dernieres Nouvelles d'Alsace reported on Saturday that among those arrested were six people who were set to plunge into the Rhine River to disrupt the ceremonial crossing of the Passerelles des Deux Rives bridge by NATO leaders.

Two of the divers taken into custody were said to be members of the pro-environment group Greenpeace. (dpa)