Nato protesters clash with police

Stacks of old tyres were also set ablaze, unleashing thick plumes of black smoke that could be seen from across the river.

Michelle Obama, wife of the US president Barack Obama, and other spouses cancelled a visit to a cancer hospital out of concern for security, the French president's office said.

Some 1,000 protesters were staked out near the hospital they were to visit.

Some of the protesters say they want an end to war and call Nato a tool of Western imperialism. Others simply appear bent on causing chaos.

The protest began calmly but began turning violent. One reporter saw police in body armour and helmets hoisting shields as they were pelted by several hundred protesters with rocks, sticks and then Molotov cocktails.

About 100 officers responded by lobbing flash bombs and volleys of tear gas into the crowds of demonstrators, many dressed in black and wearing masks or balaclavas.

Members of the violence-prone "black bloc" - named for their black clothes and hoods - then headed toward the Europa Bridge and set fire to the customs station on the French side and sprayed graffiti on the walls of buildings.

German Chancellor Angela Merkel and two dozen other Nato leaders walked across the bridge separating Germany and France before the 60th-anniversary summit began.