A suicide car bomber has killed at least 30 people in a crowded market in Talafar in north-west Iraq, police say.
Baghdad was hit be a wave of insurgency attacks
The town's police chief says the blast occurred at about 1100 (0800 GMT) when the market was full of shoppers.
Talafar, about 150km (90 miles) from the Syrian border, is a centre for Iraqi insurgents and thought to be a staging-post for foreign fighters.
Meanwhile another suicide attacker has killed at least seven people at an army checkpoint in western Baghdad.
The blast occurred at about 1200 in the Amiriya area. Most of the victims were Iraqi soldiers, police said.
Police said there were eight other attacks in Baghdad on Tuesday, including another suicide car bombing, three roadside bombs and four drive-by shootings. Five people are reported killed.
Last month US and Iraqi forces swept through Talafar to uproot insurgents, but many of them are reported to have slipped away despite claims of high death tolls and detainee numbers by the authorities.
Police chief Brig Najim Abdullah initially said the blast in Talafar had been triggered by remote control, although that view was later revised.
BBC Baghdad correspondent Caroline Hawley says the attack appears to have deliberately targeted civilians and raises the question of whether residents of western Iraq will be able to vote safely in the referendum on Saturday on the country's new constitution.
A police source quoted by Reuters news agency said emergency teams were prevented from reaching the casualties because of threats by rebel forces.
On 28 September, a female dressed in man's clothes attacked an army recruitment centre in Talafar, killing at least six people and wounding 30.
The national referendum on the new Iraqi constitution has divided the country along ethnic and sectarian lines.
Correspondents say there is support in the Kurdish north and Shia Muslim south but opposition in central and western areas where Sunni Arabs predominate.