Anne Hidalgo made the comment Thursday at the first Living Together summit, an international gathering of 23 mayors in Montreal.
They were invited by Montreal Mayor Denis Coderre to discuss combating radicalization following terrorist attacks in Paris, Copenhagen, Saint-Jean-sur-Richeleu, Que. and other cities around the world.
Hidalgo said cities are places of great inequities that are the source of frustration and can degenerate into violence and radicalization.
She said one solution is the example of schools in her city, which are open on Saturday with the help of volunteers so that youth have a place to go.
Muriel Bowser, the mayor of Washington, D.C., said cities also must fight poverty.
She suggested measures she has put forward like offering jobs to youth, affordable social housing and increasing the minimum wage.
Coderre said he would like to increase access to sports and cultural equipment.
The next summit will be held two years from now in Casablanca, Morocco.
Among the cities represented at the summit were Hiroshima, Dakar, Bamako and Beirut.
Mayors from Halifax, Quebec City and Lac-Megantic, Que. were also present.