French police have clashed with anti-Nato protesters in Strasbourg, firing tear gas and rubber bullets to stop a crowd getting to the city centre.
Masked protesters smashed bus shelters and set fire to rubbish bins. AFP reported around 100 arrests.
Security has been high in Strasbourg and across the German border in preparation for Friday's summit.
Some 25,000 police are on duty to control the tens of thousands of protesters expected to attend.
Groups of youths, many wearing hoods or scarves, walked through a suburb of the city carrying banners saying: "Stop repression in London and Strasbourg".
Bus stops and vehicles were vandalised, shop windows smashed and a barricade put up on one street.
A protestor near a burning barricade in Strasbourg
Protesters set up burning barricades in the city
One protester rammed a pole through the front window of a police vehicle.
A passenger in the car appeared to be holding a handgun as it quickly reversed.
In a separate incident, AFP reported that a German photographer had been taken to hospital after being injured in the stomach by a rubber bullet.
An eyewitness who asked not to be named told the BBC that riot vans and water cannon had seen heading towards the protesters' official camp in Ganzau, south of the city.
Leaders of Nato member states are due in the city on Friday for the alliance's 60th-anniversary summit.
France last month announced it would be fully re-integrated into Nato.
For decades it has stood at a distance from the alliance, taking part in military operations but not in its central planning and decision-making.