US President Barack Obama and his wife Michelle arrived to cheers as world leaders gathered in Strasbourg to mark Nato's 60th anniversary. President Obama and his wife were cheered by well-wishers squashed behind security barriers and he received a kiss from a woman in the crowd. The first encounter between two of the world's most glamourous women, Mrs Obama and her glamorous French counterpart, Carla Bruni, took place at the elegant Palais de Rohan. The Nato summit - which Prime Minister Gordon Brown is also attending fresh from his G20 summit success - is co-hosted by Strasbourg and the German cities Baden Baden and Kehl, on the other side of the Rhine river. Following a bilateral meeting with President Nicolas Sarkozy and a US-style "town hall" meeting with French and German youths, Mr Obama will hop across the border for discussions with German Chancellor Angela Merkel. On the top of the agenda will be the worsening crisis in far-off Afghanistan and Mr Obama will try to secure Nato backing for a new strategy he unveiled last week aimed to try to get a grip on rising violence by Taliban militants driven from power in 2001 but never completely defeated. It broadens the focus to include Pakistan and puts the highest priority on the defeat of al-Qaeda militants who Mr Obama says are plotting new attacks on the US. Earlier, violence flared in Strasbourg as protesters clashed with riot police in running battles ahead of the summit. Officers fired teargas and rubber bullets into the crowd as the violence intensified and 300 people were arrested. The city has been virtually shut down as troops and police mount one of their biggest security operations to protect thousands of delegates from 26 countries. Schools and universities are closed and residents have been given badges to allow them limited access during the two-day gathering which also marks the return of France to Nato's military command. All civilian road traffic is being diverted away from the city, and security fears have also meant the unprecedented suspension of EU rules on the free movement of citizens. The so-called "Schengen" accord has been put on hold to allow the temporary reinstatement of border controls operated by German troops and police at the bridge across the Rhine linking Strasbourg and the German town of Kehl, where some of the official Nato ceremonies will take place.