Tear gas fired at Nato protesters

Police said that several hundred protesters started to burn a makeshift barricade of slats of wood and rubbish bins on a road leading to a camp of demonstrators in the Strasbourg neighbourhood of Neuhof.

Some of the protesters said they were frustrated about the large police presence in the French city and across the Rhine river in the German cities of Kehl and Baden-Baden, where US President Barack Obama and German Chancellor Angela Merkel met.

Protest organiser Moritz Volkatz asked people to return to the camp in Strasbourg, where some 3,000 people are staying, and to wait for Saturday's planned rallies.

Christoph Kleine, a spokesman for the protest network Block Nato, said that avoiding violence was one of the protesters' goals but they would eventually get from the camp to the heavily guarded centre of Strasbourg, where the Nato summit is being held on Saturday.

"We do not want any clashes with police ... We will go around them, we will go through them," he said. "We will not attack them. But we will make our way."

Some 15,000 German police - including 31 riot squads - and 9,000 French police are on call for the summit.

German authorities had estimated that up to 25,000 protesters would take part in several demonstrations in Baden-Baden and Kehl. France's interior minister has suggested 30,000 to 40,000 ultimately could show up in Strasbourg, where the camp was set up to house demonstrators.

In Baden-Baden, about 500 people - mostly young adults - walked quietly and slowly from the main train station to the city's centre, flanked on both sides by a massive phalanx of police, some in riot gear with thick pads, protective vests and helmets and batons. Police helicopters flew overhead.

There were about 5,000 police in the city where President Obama arrived with his wife, Michelle, aboard Marine One, the presidential helicopter.