Police found sticks of dynamite tied together in a bathroom of French department store Printemps in downtown Paris. A previously unknown group reportedly claimed responsibility.
Authorities said the dynamite had no detonator and French Interior Minister Michele Alliot-Marie said it posed no danger.
But the explosives caused a stir at the height of Christmas season and Printemps staff temporarily evacuated the store.
A letter sent to the Agence France-Presse news agency warned of several bombs in the store and called for the French government to remove its troops from Afghanistan.
It identified itself as the Afghan Revolutionary Front, which Alliot-Marie said was unknown to French authorities. She also cautioned against the letter's claims, which she said could point to false leads in the police investigation.
In remarks to French radio, a former head of France's domestic security service Yves Bonnet said explosives could be meant to intimidate the French government, but also to impact public opinion about French military operations in Afghanistan.
France has one of the largest contingents in Afghanistan and President Nicolas Sarkozy decided this year to add hundreds of troops to the force.