Demonstrators from as far afield as Japan have flocked to a "counter-summit" in Strasbourg to campaign against war, defence spending and nuclear weapons, but Strasbourg's streets were virtually deserted on Friday as unauthorised traffic was forbidden in many parts of the city.
Rainbow flags saying "Peace" fluttered from windows on the outskirts of the French city, but all signs of protest had been erased from the central streets and squares, a Reuters news agency report said.
Schools and the university were closed and most businesses and restaurants have shut down for the duration of the summit.
But outside the city, police used teargas and water cannons to force back hundreds of anti-Nato protesters and two people were injured when youths let off fireworks in response to police spraying them with water, French television said.
The clashes occurred shortly after Barack Obama, the US president, addressed a US-style "town hall meeting" in the centre of Strasbourg, before leaving by helicopter for the summit's opening session in Baden-Baden in Germany.
'Like serious criminals'
Protesters at the campsite, who say they plan peaceful protests, have criticised the police tactics.
"We have been treated like serious criminals," said a German student at the campsite.
"We were searched American-style with our hands on the car, but we are going to stay calm and we are not going to hit back."
Tensions were high after police arrested about 300 people and wounded one man with a rubber bullet in clashes on Thursday. Many of those detained were later freed.
Some protesters said they were frustrated by the large police presence in Strasbourg and across the Rhine river in the German cities of Kehl and Baden-Baden, where Obama and Angela Merkel, the German Chancellor, met for the summit's opening session.
Over 20 protesters were detained, including a 22-year-old man, who police said had breached a ban on wearing face masks.
He was later freed.
Two German protesters will be prosecuted for illegally carrying arms, police there said.