Up to 24 people were killed and dozens wounded in waves of mortar barrages and bomb explosions in Baghdad on Sunday, as Iraqis voting in the country's parliamentary election, an Interior Ministry source said.

Four people were killed and six injured when a Katyusha rocket struck the dense populated neighborhood of Hurriyah in northern Baghdad, the source told Xinhua on condition of anonymity.

In separate incident, two people were killed and six others injured in a roadside bomb explosion outside a school using as voting center in Baghdad western neighborhood of Khadraa, the source said.

Two more people were killed and five others injured in a roadside bomb at Jihad district in southwest of Baghdad, the source added.

Meanwhile, separate bomb explosions wounded 12 people in Jihad and Grai'at districts in the capital, he said.

Earlier, the source said a total of 16 people were killed and dozens more injured in two attacks, including a mortar round that hit a residential building and killed 12 people.

Dozens of mortar rounds and rockets hit Baghdad neighborhoods since early in the day when polling centers opened their doors for voters for the country's parliamentary elections.

The election is regarded as a test for the country's national reconciliation and political process as it has been struggling to improve security situation in the past few years and preparing itself for a planned full withdrawal of U.S. troops at the end of 2011.