Four people were killed Tuesdayin the explosion of a bomb in a parked car in southwestern Baghdad, officals said.

The blast in a Sunni neighborhood also injured 14 people.

The information came from police and medical officials who spoke on condition of anonymity because they were not authorized to speak to reporters.

There was no immediate claim of responsibility.

Violence has decreased dramatically in Iraq since the height of the war, but bombings and shootings still happen daily across the country, many against a sectarian background.

On Sunday, 16 people were killed during a series of blasts in and around the capital. Many Iraqis worry that violence may increase when U.S. troops pull out. That is scheduled for the end of this year.

In Washington, retiring Defense Secretary Robert Gates said he hoped Iraq's government would ask the U.S. to keep its troops in the country longer than planned. He said he believed the U.S. would agree if asked.

Gates said a longer U.S. military presence could help sustain the security and other gains Iraq has made in recent years, and Iraq could become a model for a multi-sectarian society in an Arab country "that shows that democracy works."