Farhad Khosrokhavar, a sociologist at the École des Hautes Études en Sciences Sociales in Paris, said adolescent and postadolescent boys and girls were increasingly involved in jihad in Europe. “And then we have a second category, which is women,” he said.

While the extremist women operating today in France typically proclaim loyalty to the Islamic State and have been in touch with people affiliated with the group, they appear to be acting with guidance and encouragement only from afar, from men either in Syria or in Europe.

Yet there are also continuing signs of the ways in which the male-dominated nature of Islamic jihadist culture defines the relationships between male and female extremists. Recruiters encourage online betrothals, and one of the women who were recently detained in the case of the train station attack had been engaged online to two different extremists, each of whom was killed in carrying out gruesome attacks in France, Mr. Molins said.

These somewhat contradictory elements suggest that the threat is coming from a more independent, feminist type of jihadist, who sees herself as acting similarly to a man, but at the same time, some in this category of women also appear to be acting on instructions from male counterparts in the Islamic State. In both cases, there is the possibility, experts say, that the Islamic State and other groups are using women to goad men into staging attacks.

Recent comments made by Rachid Kassim, a Frenchman who joined the Islamic State and is now suspected of being one of its leading propagandists, suggest this kind of strategy might be at play.

“Women, sisters are going on the attack,” he wrote on the Telegram messaging application last month, after the gas canister plot was thwarted, according to the newspaper Le Monde. “Where are the brothers?” he added. Mr. Kassim is suspected of encouraging the women in that plot.

The recent plots in France led by women show both determination and the limits of their efforts. They also highlight what these women have in common: Some are converts, and some have tried to go to Syria but have been turned back. And the younger ones, especially, seem emotionally troubled, said Wafa Messaoud, a Muslim chaplain, who works with Muslim women in French prisons.