Loud explosions and gunfire have rocked Nigeria's northern city of Maiduguri, which has seen growing violence by the militant Islamist group Boko Haram.Details are unclear, but reports said at least 10 people had been killed, including several soldiers.A primary school and a radio tower were reportedly set ablaze.Earlier this month witnesses said soldiers shot dead up to 30 civilians after a bomb attack on an army patrol in Maiduguri.In the latest incident, reports said soldiers sealed off nearly every street in the city centre as the attacks began on Monday afternoon and continued after dark.Witnesses said that, earlier on Monday, a gunman had shot dead a traffic warden in the city close to a military checkpoint.In the incident earlier this month, soldiers in Maiduguri reportedly opened fire on a busy street after a bomb attack killed an army officer.Shops and homes were also torched, witnesses said.The army denied killing civilians although correspondents say it offered contradictory explanations about what had happened.Attacks in central and northern Nigeria blamed on Boko Haram have killed some 1,400 people since 2010.The sect wants to impose Sharia law across the country.