It was perhaps not what Michelle Obama expected on her first presidential foray to France. But it was certainly French.

Anti-war and anti-capitalist protesters tangled the streets of the Alsatian city of Strasbourg and thwarted her planned visit to an anti-cancer research centre with other spouses of NATO leaders.

Police barricades and narrow pedestrian streets that wind through the city centre meant she couldn't get there and back by motorcade.

So the visit was shelved, and they had an unplanned coffee with the French first lady instead. A few kilometres (miles) away, Molotov cocktails and tear gas canisters exploded as protesters pushed back riot police, filling the spring air with smoke and acrid stench. Nearby, 28 NATO leaders met to choose a new chief for the alliance and seek answers for Afghanistan.

Such violence is not all that common here. But marches, strikes and demonstrations are a standard form of public expression in France, and cars are regularly burned on the weekends in Stasbourg's poorer neighborhoods.

Michelle Obama and the other spouses stuck to their main event of the day: a visit to a 15th century cathedral that is a UNESCO-protected monument in the historic city centre.