A roadside bomb targeting a US military convoy exploded near a civilian bus in the southern oil hub of Basra today, killing six people and wounding a dozen others, provincial officials said.
The bomb went off near a prison in the al-Maaqal district of northern Basra, deputy governor Ahmed Hamid said.
"A roadside bomb exploded near a civilian bus," Mr Hamid said. "Most of the casualties are civilian. The explosion happened near the prison and was targeting a US patrol."
US troops surrounded the scene of the blast along with Iraqi security forces, according to Reuters television footage, which showed blood-spattered bus windows and debris strewn in the streets.
"Many were killed," a witness said. "I saw the decapitated body of a woman and I helped a wounded man, bleeding, out of the bus." "I blame government for this incident. What has this government done to us?" he added.
Many of the victims were women and children, said Ali al-Maliki, the head of the Basra provincial council's security committee.
There were no immediate reports of US casualties among the dead and wounded.
A second bomb exploded near a US convoy in another area of northern Basra today but no one was hurt.
Basra, located about 420 kilometres southeast of Baghdad in the centre of Iraq's main oil producing region, has seen several large demonstrations in recent weeks as protests inspired by uprisings across the Arab world have shaken Iraq's federal and local governments.
On Friday, Iraqi security forces used water cannon and batons to disperse protesters at a rally to pressure the government for more jobs, more electricity and better services.
While violence in Iraq has fallen sharply since the height of sectarian slaughter in 2006-07, a weakened but still lethal insurgency carries out attacks daily. US forces are scheduled to withdraw by the end of the year.