A suicide bomber blew up a tanker truck at police headquarters in the Iraqi city of Tikrit Monday, killing seven people in the latest in a spike in unrest ahead of the first elections since 2010. Eleven people were also wounded in the 8:40 am (0540 GMT) bombing in the city, hometown of executed dictator Saddam Hussein and remains a focus for insurgents, police and medics said. Most of the casualties in the city 160 kilometres (100 miles) north of Baghdad were police, the sources added. The bombing comes ahead of provincial elections scheduled for April 20, due to be held in 12 of Iraq's 18 provinces, the country's first polls since a parliamentary vote in March 2010. But questions have been raised over the credibility of the polls as they have been postponed in two provinces roiled by months of protests, and 11 candidates have been killed, according to an AFP tally. Although markedly lower than its peak in 2006 and 2007, levels of violence remain high in Iraq -- at least 274 people have been killed in attacks this month, the highest figure since August 2012.