Separately, up to seven people were killed and 10 others injured when a suicide car bomber blew up his explosive-laden car in the afternoon near a fuel station in the Shiite neighborhood of Shula, an interior ministry source said.

What's more, five people were killed and eight others were wounded in a rocket attack on the Kamaliyah neighborhood in eastern Baghdad.

Those incidents were preceded with a rocket shelling on the sprawling Green Zone in central Baghdad around 6:00 A.M. (0300 GMT) .

Emergency sirens could be heard in the highly protected area which houses the government offices and diplomatic mission facilities, including the US embassy. No casualties were reported.

Insurgents frequently targeted the Green Zone by mortars and rockets. The roughly 10 square km area is located on the west bank of the Tigris River which bisects the Iraqi capital.

In Diyala province, the Iraqi police said that US helicopters pounded four houses in the town of Baladruz, some 100 km northeast of Baghdad, killing 12 civilians and wounding five others.

Most of the victims were women and children and the targeted houses were badly damaged, according to a police source.

There was no immediate statement from the US military but media reports quoted a US military spokesman as saying that the attack targeted a "suicide bombing network", killing 12 men, six of whom were believed to be suicide bombers.

The US and Iraqi troops have launched a series of operations in Diyala province during the past months to uproot militants of al-Qaida in Iraqi network.

Waves of explosions since the beginning of this year rocked the lull of violence achieved in the second half of last year.

The latest uptick of attacks also came as David Petraeus, chief commander of the US troops in Iraq, and US ambassador to Iraq Ryan Crocker are expected to report to the Congress the Iraqi situation early next month.

Petraeus has said a period of time is needed after the planned drawdown of five brigades by July to consolidate the hard-fought security gain and evaluate the outcome.

The US military said al-Qaida remains the principal threat to the security in Iraq despite that the terrorists had suffered a major defeat.