French police fired teargas and water cannon to force back anti-Nato protesters on the outskirts of the French city of Strasbourg and cordoned off the city centre before alliance leaders began a summit today.
Police arrested 300 people overnight, cleared the city centre of protesters and peace flags, and cut off public transport to a campsite housing thousands of demonstrators.
About 100 people dressed as clowns staged a demonstration near the campsite, but were pushed back by police, a witness said.
Police then sprayed water to disperse a crowd of youths from a nearby suburb, and the youths let off fireworks. French television said two people were injured.
The clashes were shortly after US President Barack Obama 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 on Germany, the event's co-host.
Protesters said tensions had risen after police wounded one man with a rubber bullet in clashes with hundreds of anti-Nato activists and youths from the suburbs yesterday.
"We have been treated like serious criminals," said a German student at the campsite who identified himself as Michael.
"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."
In Baden-Baden, where leaders held a working dinner, police said they had detained a 22-year-old man for breaching a ban on wearing face masks. He was later freed.
Up to 500 people took part in a peaceful demonstration in the German town, local police said.
France and Germany have each deployed 15,000 police and troops in an operation costing €110 million.
Organisers of the mainly peaceful anti-Nato movement have said they will try to derail the summit by blocking roads and marching into Strasbourg where the main sessions will be held on Saturday, challenging a security cordon set up to keep them out.
Christoph Kleine, a spokesman for the Block Nato movement, said protesters would attempt to leave their camp on the outskirts of the city early tomorrow, defying police restrictions, but said they did not plan to commit violence.
Pacifists from as far afield as Japan flocked to a "counter-summit" in Strasbourg to campaign against war, defence spending and nuclear weapons as the 28-nation, former Cold War military alliance marks its 60th anniversary.
Rainbow flags saying PACE ("peace") fluttered from windows on the outskirts of Strasbourg, but all signs of protest had been erased from the central streets and squares. Many shops were shuttered and the streets were almost deserted.
Police said they had released most of the 300 protesters arrested yesterday, when masked youths smashed windows, barricaded a street and at one point hurled a pole through the windscreen of a military vehicle.
Two German protesters will be prosecuted for illegally carrying arms, and some 20 protesters are still being held.
One man was briefly sent to hospital yesterday after being hit in the chest by a rubber bullet, city authorities said.
Reuters