The attacks came on the second day of campaigning for April 30 parliamentary polls, Iraq's first since March 2010.
Violence is at its highest since 2008 and the country is still struggling to rebuild its battered economy and infrastructure after decades of conflict.
UN special envoy Nickolay Mladenov, in an interview with AFP, underscored fears the polls could worsen a long-standing political deadlock in which Iraq's fractious national unity government has passed little in the way of significant legislation.
The attack struck in Riyadh, a mostly-Sunni town in ethnically mixed Kirkuk province.
Also Read
Elsewhere in Kirkuk, bombings targeting the military killed six soldiers and wounded 14 others, while attacks in Kut, south of the capital, and the main northern city of Mosul, left two policemen dead.
Another policeman was killed in a firefight with militants south of Baghdad in a confessionally mixed region known as the Triangle of Death for the frequency of attacks that take place there.
But campaigns are rarely fought on individual issues, with parties instead appealing to voters' ethnic, sectarian or tribal allegiances or resorting to trumpeting well-known personalities.
A lack of effort at cross-sectarian politics could, Mladenov said, be a major issue.
"Campaigning will be highly divisive," he told AFP from his office in Baghdad's heavily fortified Green Zone complex.
"Everyone is ratcheting it up to the maximum, and you could see this even before officially the campaign started."
"The efforts to reach across the sectarian divide are very weak.