PARIS?- Projectile-throwing youths clashed with police in two French cities on the sidelines of demonstrations Saturday honoring a protester who was killed during a similar confrontation over a dam project last week.

Riot police bearing shields fired tear-gas canisters in western Nantes to disperse masked protesters?- some of whom lit fires, chucked back the canisters, and tore down street signs to use as projectiles. Similar unrest broke out in southwestern Toulouse, where authorities said some rioters among mostly peaceful protesters smashed bank windows and tore up public property.

The demonstrations testified to growing tensions between angry youths and police on the margins of mostly peaceful rallies by environmental activists in recent months. A long-running standoff has involved foes of an airport project in Nantes and more recently, green groups have protested against the Sivens dam project in southwestern France.

Saturday's rallies were called to honor Remi Fraisse, a 21-year-old protester who died last week in clashes between police and demonstrators near the southwestern town of Lisle-sur-Tarn, not far from where the dam is to go up. Such rallies?- first primarily about environmental causes?- have for some morphed into protests about alleged police brutality.

Hundreds of riot police and officers were mobilized in the two cities. The local government office said at least two protesters were injured Saturday in Nantes, as were two police officers _ one burned by acid that was allegedly thrown by a rioter. At least 16 people were arrested there.

In Toulouse, one police officer was slightly injured and eight demonstrators were detained, the local government office said in a statement.

Authorities denounced the violence Saturday and called for a return to calm.

French President Francois Hollande has called for an investigation into what caused Fraisse's death, and an autopsy found that a large wound on his back was caused by some kind of explosion.