Gunmen attacked a police station on voting day Saturday in Nigeria's restive oil region, killing seven police and leaving the building in ashes, police said. Rivers State police spokeswoman Irejua Barasua confirmed the attack, but had no more details. Angry security forces milled around outside the charred police station in the main southern city of Port Harcourt, according to AP. A spokesman for an armed gang in the region led by notorious gunman Ateke Tom claimed credit for the attack and said others had been launched in other regions of Nigeria's vast southern wetlands. No details were available. Many criminal and militant elements in the region are opposed to the vote, saying they helped local politicians rig a 2003 election and received nothing in return. Voters were electing their state legislators and governors Saturday as Nigeria struggles to cement civilian rule. Presidential elections are scheduled for April 21, setting up the country's first-ever transfer of power between elected leaders since independence from Britain in 1960. All other votes have been scuttled by coups d'etat or annulments. Nigeria is Africa's largest oil producer, but most people are mired in deep poverty across the country's south, where the petroleum is pumped. They blame corrupt officials for their predicament and militancy has flourished in the region of swamps and creeks. A year of stepped-up violence has seen more than 150 foreign workers kidnapped and production cut by nearly one quarter, helping send oil prices higher around the world. -- SPA