Police fear tear gas into a market in Sanabis on Thursday
At least 13 candidates, most of them Sunni, have been slain.
Saturday's election to select provincial council members is seen as a measure pf strength of the largely-Shia national government before the Parliamentary elections in 2014.
No group claimed responsibility for the weekend attacks in Baiji town, 180 kilometres (112 miles) north of Baghdad.
Another Sunni candidate escaped a roadside bomb in Balad Ruz, 90 km (55 miles) northeast of the capital, on Sunday.