Guerrillas shot dead 17 Iraqis working for US forces north of Baghdad yesterday and killed six other people, including three Iraqi National Guards.
Insurgents have carried out a number of attacks in Sunni areas since Friday, mainly targeting Iraqi security forces and civilians working with the US military, taking the death toll in the past three days to over 70.
US marines said gunmen in two cars opened fire on two civilian buses carrying Iraqis to work at an arms dump outside Saddam Hussein's home town of Tikrit on Sunday, killing 17 Iraqis and wounding 13 others.
A suicide car bomber detonated his vehicle beside a National Guard convoy in the rebel stronghold of Baiji, north of Tikrit, killing local a National Guard commander and three of his bodyguards.
Later on Sunday, gunmen killed two National Guards and wounded four others in an attack near Latifiya, a town south of Baghdad that has seen persistent unrest, officials said.
On Saturday, a suicide bomber targeted a bus carrying Kurdish peshmerga fighters in the city of Mosul, 240 miles north of Baghdad, killing 16 people, Kurdish officials said. The peshmerga have been helping secure Mosul since most of the city's police fled after an insurgent onslaught last month.
Two suicide bombers also struck at a police station just outside the fortified Green Zone in Baghdad, killing seven people and wounding more than 50.
At least six US troops have been killed since Friday.
Two were killed in an ambush in Mosul Saturday, two by separate roadside bombs earlier in the day, and two by a suicide car bomb at the Jordanian border on Friday.
The surge in violence has fuelled fears that Iraq's first democratic elections in decades, scheduled for the end of January, could be derailed by guerrilla attacks and intimidation.