Strasbourg, France  - Rioters set fire to a five-storey hotel and other buildings in Strasbourg Saturday as left-wing protests against a NATO summit in the French city turned violent.

Fire also gutted a pharmacy, a nearby tourist information office and a disused French customs post in the city near the German border.

Police said 10,000 people had demonstrated against NATO on the French side, most of them peacefully. But because of the mayhem, police scotched plans for another 6,000 activists from the German side to march over the border bridge and join the main rally.

French police estimated only 1,000 had been violent. Security sources said some of the rioters, believed to be mainly anarchists dedicated to bringing down the Western system, had been carrying loaded guns when police arrested them.

The hotel fire, apparently caused by petrol bombs, spread through the ground floor of the building, which had been vacated because of the summit, and then took hold up to the roof.

It was not known if there were any casualties in the fire, but witnesses said no ambulances had been called to the scene. The protests as a whole saw 34 demonstators injured, with 18 requiring treatment in hospital. Eight police were also slightly injured.

One French police officer claimed the hotel was attacked in the belief that it was being used to accommodate out-of-town police.

"It's no coincidence," he said bitterly. Police spokesmen declined to say if officers had been staying in the 78-room hotel, close to the broad Rhine River which marks the French-German border.

French riot police, armed with clubs and shields, repeatedly fired tear gas grenades to drive off rioters.

Frightened French firefighters fled over the bridge to take refuge in Germany as the violence got out of hand, while German police occupied the traffic bridge to prevent the rioters from seizing it.

The violence on the French side ended when the militants melted away into the city. Police said 10 demonstrators were injured in the clashes and there had been a large number of detentions.

European pacifists, anarchists, communists and radical feminists from several nations had formed a protest alliance before the summit.

Many were avowedly non-violent, but the movement also embraced a hardline group that has repeatedly clashed with police at summits and other government events in European nations down the years.

NATO leaders were meeting in Strasbourg on Saturday at a summit celebrating the 60th anniversary of the alliance's founding.

Sporadic clashes Thursday evening and Friday evening had given a preview of Saturday's attack by the militants, many of them carrying stones, empty bottles and petrol bombs to throw.

The militants wore black clothing as a kind of uniform and ski masks to conceal their faces from police video cameras.

Some 10,000 French police officers and gendarmes, reinforced by some German police units, were deployed in and around Strasbourg.

The day of manoeuvring began early Saturday as nearly 2,000 demonstrators managed to infiltrate the city, blocking tramway and bus routes. But they failed in their primary goal of blocking the motorcades carrying NATO leaders through Strasbourg.

The demonstrators' motto was a call to spend "millions on peace instead of billions on war." (dpa)