At least 13 of the 33 were police officers, police said. No one was killed in the fourth Baghdad car bombing.

Speaking at a news conference on Thursday, US Maj. Gen. Rick Lynch described the surge of attacks as insurgents’ attempt to prevent the process of forming a national unity government.

Political leaders are still quarreling over the new government's makeup and they plan to hold a meeting on Saturday to discuss their differences.

The violence comes a week after the US military announced Operation Scales of Justice, designed to increase the number of police officers and troops on Baghdad's streets.

Amid the attacks, a Multi-National Forces Iraq operation rescued three kidnapped Christian aid workers in Baghdad who had been held for nearly four months.

The day's deadliest bombing targeted the Baghdad Police Major Crime Unit in the central part of the capital, killing 23 people, including 10 police officers. The attack wounded another 35 victims, police said.

Earlier, a car bomb ignited near a police checkpoint in central Baghdad, killing three police and injuring six other people, including a police officer and five civilians, police said.

Another car bomb exploded in a busy market near a Shiite mosque in southwestern Baghdad, killing seven people and wounding 22 others.

BBC