Seventeen civilians have been shot dead and 13 wounded by guerrillas in the northern Iraqi city of Tikrit.
Gunmen in two cars opened fire on two buses that were taking workers to a weapons dump.
The workers were employed in the disposal of unexploded ordnance.
In another attack, a suicide car bomber drove into an Iraqi National Guard checkpoint in Beiji, about 75 miles north of Tikrit, killing three soldiers and wounding 18.
It comes as the head of the US Central Command in Baghdad, General John Abizaid, expressed concern about the ability of Iraqi forces to cope with security without US support, in the run-up to elections in January.
Two US soldiers were killed and four wounded in an attack on their patrol in the northern Iraqi city of Mosul overnight.
Return of British regiment
In another development, British troops from the Black Watch regiment are expected to return home from Iraq within the next week after a month supporting American forces near Baghdad.
The 850-strong group has returned to its base in Basra in southern Iraq.
Five soldiers were killed during the deployment.
