The men, from Orleans, had been arrested and detained in Pakistan for several months for entering the country illegally from Iran, Radio France Internationale reported Friday.
An investigator said the men, ages 27, 29, and 30, had gone to Pakistan to study Islam and to fight in Afghanistan.
They had told their families they were going on a pilgrimage to Mecca when they left France in January 2012. They were detained in Pakistan five months later.
A fourth man arrested with them, Naamen Meziche, was believed to have links to al-Qaida, RFI said.