The roadside explosive device blew up when US vehicles were transporting equipment in west Baghdad on Sunday morning.
The bomb set a vehicle ablaze, eyewitnesses told Aljazeera. Occupation forces immediately closed the area and began searching for the attackers, the eyewitnesses added.
On Saturday night, the US headquarters in al-Huwija, northeast of Baghdad, came under rocket attack, according to our correspondent in the capital.
US forces fired flares in an attempt to search for the attackers. No casualties have yet been reported for either incident.
The US military also reported Sunday that a soldier drowned and two more were lightly injured when their vehicle fell into a canal near Saddam Hussein's home town of Tikrit. The death brings to 78 the number of US soldiers who have died in circumstances Washington attributes to "non-combat" activities.
In Najaf, which is preparing for the Tuesday burial of assassinated Shia cleric Ayat Allah Muhammad al-Hakim, tragedy returned to claim the lives of two civilians.
Bodyguards of Shia cleric, Muqtada Sadr - an outspoken critic of US occupation - opened fire on a car at a checkpoint in Najaf, killing two and wounding two more.
Haidar Abbas, admissions officer at the city hospital, said: "Sadr's people had set up a checkpoint on the road. When the driver saw the roadblock, he thought the bodyguards were thieves and accelerated when the guards opened fire."
Sadr's security has increased in light of the double car bombing on Friday that killed Muhammad al-Hakim and 82 others.
Change in policy
The attack is the latest in a campaign of resistance which has forced the United States-led occupation forces to moot handing over policing to Iraqi militias, the New York Times reported Sunday.
All paramilitary recruits will have been already screened for links to former president Saddam Hussein’s government, according to the newspaper.
Some Iraqi exiles working with the US Department of Defence said militias could form a force of several thousand men, most with military experience, and be ready to take over policing in just over a month's time.
Mukhtar Shukhat, a prominent exile who took part in discussions with the US-led occupation administration on Saturday, said: "The situation has changed, and there is a new receptiveness to the idea."
Charles Heatley, a spokesman for the Coalition Provisional Authority, said: "Efforts to provide security in this country should be unified and they should be recognised as Iraqi security forces.”
A Shia cleric, Said Nail Musawi, told US soldiers guarding the US-appointed Coalition Provisional Authority in Baghdad: "The knife is at our neck. I don't know how much longer I can control my people."
The question of whether the paramilitary groups are the security solution will also raise another controversy. Unresolved questions remain as to whether Americans or Iraqis would be in command of the forces.
With such a short time frame, another concern reported by the Times would be how to prevent unregulated, untrained bands of armed men under separate commands policing Iraq.
Several US officials told the newspaper of their fears that various factions making up the militia groups could end up attacking one another.