MAIDUGURI, Nigeria (AP) — In fierce fighting Sunday, Nigerian troops clashed with Islamic extremists who attacked Maiduguri, the biggest city in northeast Nigeria. "Coordinated air and land operations are being conducted now," Defense Ministry spokesman Brig. Boko Haram has denounced democracy and is fighting to impose its strict version of Shariah law across Nigeria, whose population of about 170 million is divided almost equally between Muslims in the north and Christians in the south. Maiduguri is the birthplace of Boko Haram and has been attacked many times in the five-year Islamic insurgency that killed 10,000 people last year.