Bomb attacks on Sunni Muslim worshippers in Baghdad and north of the Iraqi capital killed 12 people on Friday, officials said, the latest in an uptick in violence ahead of provincial polls next week. In the deadliest single blast, a roadside bomb struck after prayers at the Omar bin Abdul Aziz mosque, in the town of Kanaan in restive Diyala province, a police colonel and a doctor said. Overall, 12 people were killed and 30 others wounded, the sources said. Two more bombings, in Baghdad and another town in Diyala, one near a Sunni mosque and the other as Sunni worshippers were returning from mid-day prayers, wounded seven people. Also on Friday, police near the main northern city of Mosul found the corpses of two policemen and a soldier, all three with gunshot wounds to the head and chest. The group had been kidnapped a day earlier. Iraq is to hold provincial elections on April 20, its first polls since 2010. Attacks on candidates have left at least a dozen election hopefuls dead, according to an AFP tally. That, and the fact that only 12 of Iraq\'s 18 provinces will vote due to a government postponement, has raised questions over the credibility of the polls. They come with the country mired in a political crisis that has pitted Prime Minister Nuri al-Maliki against several of his erstwhile national unity cabinet partners, and after more than three months of anti-government protests by the Sunni Arab minority. Violence killed 271 Iraqis last month, the highest monthly figure since August, according to an AFP tally.