Nigeria's extremists invaded a second country in the region Friday, attacking two towns in a part of Niger that is already home to tens of thousands of refugees who have fled the terror group's attacks back in Nigeria, AP reported. The expansion of Boko Haram's reach came as neighboring countries are fighting back with ground troops and aircraft, with even greater military strikes by more countries planned. Boko Haram has openly threatened to attack other countries taking part in the military effort to subdue their insurgency, blamed for 10,000 deaths over the past year. Cameroon, Niger, Chad and Benin all have pledged to send troops to fight Boko Haram, which has waged a five-year rebellion against the Nigerian government. On Friday, soldiers from Niger and Chad fought an hour-long battle that caused Boko Haram fighters to withdraw from Bosso, leaving the Niger town's streets deserted, said Abba Hassan, a local pharmacist.