Security was heightened in France after the French military began helping to repel the Islamist advance in Mali. The Islamist militants warned that France would pay a price for its intervention in Mali. President Hollande said France would not give in to “terrorist blackmail.” The Foreign Ministry stepped up security in Mauritania, Niger, and the Malian capital of Bamako; eight French nationals are being held hostage by Islamists in the Sahel.