Ansaru has taken a more hostile attitude toward France. It said the abduction of Collomp was in response to the French government's stance on Islam -- including the ban on the wearing of the veil in public and in French schools.

Boko Haram is more focused on what it sees as discrimination against Muslims in Nigeria.

Recently, like the Pakistani Taliban, it has extended its attacks to target doctors and health workers involved in polio vaccinations.

The emergence of two apparently resilient terror groups in northern Nigeria, and the surge in attacks on foreigners, pose growing challenges for a government and military already struggling to exert their authority across large areas of Africa's most populous nation.