There was the parked car stuffed with gas canisters near the Notre Dame Cathedral, a possible effort to set off an explosion in the heart of Paris. There was the suspected plot to attack a train station in the Paris area. There was the effort by one of the Islamic State’s most prominent propagandists to recruit two young people in Nice, where an attacker had killed 86 people in July by running them down in a truck.

In France, where terrorist threats have become distressingly commonplace, these three episodes, all in the last month, stood out for one reason in particular: Radicalized women were at the heart of each.

It is not yet clear whether the phenomenon is a blip or the beginning of a trend in which women play a more active role in plotting and carrying out attacks on the West.

Security officials say they are concerned, and they are seeking to understand whether women are beginning to step up because so many men are under surveillance or in detention, or whether recruiters from terror groups are urging women on, in part, as a way to shame more men into taking action. They also wonder if it is part of a strategy to make Europeans feel that they should fear men and women alike.