A truck bomb exploded near the Australian embassy in central Baghdad at about 7am (0400 GMT) on Wednesday, police and witnesses said, in a blast that rocked the centre of the city.
Two Australian soldiers were slightly wounded, an official at the embassy said.
US troops and tanks sealed off the area, which was strewn with parts of flaming wreckage.
An Iraqi guard at the nearby Australian ambassador's residence said a man drove a truck to the cement barriers in front of the embassy, then fled in another car that was waiting for him.
The truck then exploded, said the guard, who only identified himself as Hasan.
In Australia, a spokeswoman at the Department of Foreign Affairs said no Australian diplomatic staff or soldiers were injured.
Australia moved its embassy into Baghdad's Green Zone - the heavily fortified precinct that is home to the interim government and US authorities - last year.
Many were hurt in the three
explosions on Wednesday
A car bomb in north-central Baghdad came about 30 minutes after the bomb at the embassy.
That explosion happened near the al-Andalus traffic circle at the edge of the Baghdad neighbourhood of Karrada and killed six people, an interim interior ministry official said.
Army base targeted
A third car bomb killed two Iraqi security guards near Baghdad's international airport, and a fourth exploded at 8.30am local time, killing two civilians and two Iraqi soldiers at a military complex in Baghdad.
Iraqi journalist Ziyad al-Samarai told Aljazeera the explosion targeted the biggest headquarters of the Iraqi National Guard in central Baghdad.
A bomber drove through the southern gate of the former al-Muthanna airport - now a military base - and blew up his vehicle at the checkpoint, Aljazeera learned.
"Military officials extend their condolences for this unfortunate incident"
US military statement on the killing of two civilians
Five people were injured and taken to the al-Yarmuk hospital in Baghdad.
A police source said another bomb also exploded at a Baghdad bank, targeting police as they collected their salaries. Witnesses said at least one person was killed.
The US military said soldiers on Tuesday opened fire on a car as it approached a checkpoint in northern Iraq, killing two civilians in the vehicle's front seats. Six children were in the backseat.
US troops trying to stop the car used hand signals and fired warning shots before firing at the car, killing the driver and front seat passenger, a military statement said on Wednesday.
The shooting occurred in the city of Tal Afar, about 60km west of Mosul.
It was not clear from the military statement whether the two victims were the children's parents.
"Military officials extend their condolences for this unfortunate incident," the statement added.