An Al Qaida-linked website has called for the assassination of President François Hollande and French soldiers because of France's military interventions in Mali and the Central African Republic.
Sources close to the president promised "extreme vigilance", while declaring that such threats were nothing new.
"It's not the first time there have been threats," a source close to the French presidency said on Tuesday after the Islamist website The Media Platform of the Mujahideen swore that "neither Hollande, nor his soldiers will know peace in France until the Muslims of Mali and the Central African Republic (CAR) have it".
"To our lone wloves in France, execute the head of atheism and criminiality," it declared. "Terrorise his cursed government, blow them up and make them experience horror."
Similar threats were made when the Mali intervention began, a source close to Hollande told the AFP news agency on Tuesday, adding that sometimes dangers that are not announced in public are more serious.
But, the source insisted, "We are extremely vigilant".
The jihadhi site's language recalled that of Al Qaida chief Osama bin Laden after the 9/11 attacks on the US.
It accused France "ethnic cleansing and murderous crusades" in the CAR, where France has intevened against a background of the collapse of the state and sectarian violence between Christians and Muslims.
The site called on sympathisers to emulate Mohammed Merah, the Algerian-origin man who murdered three soldiers, three Jewish children and their teacher in 2012.