Boko Haram's second attempt to take the major northeastern Nigerian city of Maiduguri in a week was defeated Sunday, leaving an estimated hundreds of fighters and around a dozen civilians dead, the Associated Press reports.

The militants attacked the city of 2 million, to which another 200,000 refugees have fled from the surrounding area, on four fronts, the AP reports. About a dozen civilians were mistakenly killed by Nigerian military operations, according to witnesses who spoke to the AP on condition of anonymity "for fear of retaliation from the military."

According to Amnesty International, Boko Haram holds around 130 towns and villages, The Guardian reports. The group declared an Islamic caliphate in August. According to the U.S. Council on Foreign Relations, in the past year about 10,000 people have died in Boko Haram's attacks; in the first four years of its uprising, about 2,000 died.

Sunday's assault came after African Union leaders authorized the creation of a multinational force of 7,500 to fight the Islamist group.