Four car bombs have exploded in mainly Shi'ite areas of the Iraqi capital, killing at least 13 people and wounding more than 70 others.

Authorities say the first blast Tuesday in Baghdad's Sadr City hit a group of laborers waiting for work. The bombing killed at least eight people and wounded more than 20 others.

Another explosion in the same district killed at least two people and wounded at least a dozen more.

Two bombs exploded later in northern Baghdad, killing three people in the city's Shula and Hurriya districts.

Attacks against Shi'ite areas have killed more than 100 people in the past month, as a political crisis continues in the Shi'ite-led unity government.

The main Sunni-backed faction, Iraqiya, accuses Shi'ite Prime Minister Nouri al-Maliki of monopolizing power in Shi'ite hands. Iraqiya has boycotted the Cabinet.