Blast destroys police station in north Nigeria KANO, Nigeria (Reuters) - A powerful blast destroyed a police station in the northern Nigerian city of Kano, a senior police official said, the latest in a series of blasts in the country's second biggest city since Islamist insurgents stepped up their campaign there. The explosives also affected some surrounding buildings. It was a big bang. For now, I can not say how many of our men are affected or whether the bomber died," the police source said. Islamist sect Boko Haram claimed responsibility for a coordinated series of gun and bomb attacks in Kano Friday that killed 186 people in their deadliest strike yet. The new focus on Kano, an ancient city once at the heart of caravan routes connecting Africa's interior with the Mediterranean, underscores the sect's growing ambition. Gunfire was also heard there early Tuesday, witnesses said. From drive by shootings and petrol bombings in its northeastern heartland in Maiduguri, Boko Haram has spread across the north and have struck the capital Abuja. The Islamists have killed at least 935 people since it launched an uprising in 2009, including more than 250 in the first weeks of this year, Human Rights Watch said Tuesday. The sect focuses its attacks mostly on the police, military and government, but has increased its attacks on Christian institutions. The United States-Nigeria binational security commission met Tuesday. Discussions included the latest Boko Haram attacks and finding ways to stem the violence, diplomatic sources said. The commission usually meets at least once a year. "Jonathan's inability to respond effectively, or articulate a credible strategy, reinforces the growing perception of a deep leadership void in Abuja," London-based risk adviser Eurasia Group said in a research note Tuesday.