French security troops are to guard the fronts of all Catholic and Protestant churches for the coming Easter weekend, a memo to officials said on Thursday.
France wants to bolster its security after raising its threat alert to the highest level after the Moscow concert hall attack that claimed at least 143 lives.
The massacre was the deadliest attack in Russia in two decades, with ISIS claiming responsibility.
In a memo sent to prefects on Thursday and seen by AFP, Interior Minister Gerald Darmanin said the "very high" level of terrorist threat and persisting international tension, including the Gaza war and the Moscow attack, mean that "extreme vigilance must be maintained" during the Easter celebrations.
Mr Darmanin asked prefects to post police in front of "all" Catholic and Protestant churches, in particular during services on Friday and this weekend.
He said "particular attention" should be paid to vehicles parked near places of assembly or worship.
Two planned attacks have been foiled in France since the start of the year.
One involved a plot to stage "violent action against a Catholic religious building" by a man "clearly committed to [extremist] ideology", according to the national anti-terrorist prosecutor's office.
Gunmen open fire in Moscow concert hall - in pictures
The man, 62, was arrested and remanded in custody in early March, prosecutors said.
Catholics and Protestants celebrate the resurrection of Jesus on Easter Sunday, while Orthodox Christians hold their Easter on May 5.
