Monuments including One World Trade Center in New York, the San Francisco City Hall and Toronto's landmark CN Tower were lit red, white and blue in solidarity with France after attackers killed at least 127 people in Paris.
The World Trade Center lights were a powerful symbol of U.S. friendship and support for the French, made from the tallest building in the United States, which was built on the site of the 9/11 attacks on New York.
Infographic: Seven deadliest attacks in Europe in decades
New York police went on heightened alert, deploying counter-terrorism reinforcements to crowded places and outside the French mission to the United Nations, and the French consulate.
The New York police department said the reinforcements were made “out of an abundance of caution” to reassure the public.