The UN envoy to Iraq meanwhile urged the country's feuding leaders to meet to resolve long-running political crises that have paralysed the government and been blamed for its inability to halt the bloodshed.
As of Tuesday, 530 people have been killed and more than 1,300 wounded in May, making it the deadliest month in at least a year, according to AFP figures based on reports from security and medical sources.
Attacks in Baghdad, including a bomb that exploded on a bus in the Shiite Sadr City area in the capital's north, killed at least six people and wounded more than 30, officials said.
North of the capital, a suicide truck bomber killed four people and wounded eight in Tarmiyah, and three relatives of the deputy head of the Salaheddin provincial council were gunned down near Baiji.
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In Mosul, four police and four gunmen died in clashes, and gunmen also shot dead a tribal sheikh in the northern city.
And a bombing near Mosul killed police intelligence officer Lieutenant Colonel Faris al-Rashidi and wounded three other police, while a suicide bomber driving an explosives-rigged vehicle killed a soldier and wounded two south of the city.
The attacks come a day after a wave of violence, including bombings in Baghdad that mainly targeted Shiite areas, killed 58 people and wounded 187.