A suicide bomber blew up his car in a Baghdad square Sunday, killing four people in the first significant suicide bombing in the capital in weeks. More than a dozen Iraqis died in other attacks across the country, including a bombing that killed a police colonel and four children.

Still, with the death toll among American service members in the Iraq war approaching 2,000, the U.S. military said it has hampered insurgents' ability to unleash more devastating suicide bombings with a series of offensives in western towns that disrupted militant operations.

"We have interrupted the flow of the suicide missions into the large urban areas. Certainly, we have had success denying free movement of car bombs into Baghdad," Brig. Gen. Donald Alston told reporters in the capital.

"It is also a function of Iraqi citizens who have come forward, and with their support we have found car bomb factories. We have found a series of large weapon caches," he said.

In Sunday's attack in Baghdad, the bomber plowed his explosives-laden car into two police vehicles in downtown Tahrir Square at 11:30 a.m., killing two police officers and two civilians. U.S. troops rushing to the scene in Humvees found bystanders tending to 11 wounded people.

In the past, Baghdad has been heavily battered by suicide attacks, with a string of them killing nearly 700 people from April 1 to early September. But after an intensified security clampdown, the number of suicide car bombings across the country has fallen in recent weeks, and those that have occurred have caused fewer casualties.

Roadside bombings hit three U.S. convoys in Baghdad on Sunday morning, wounding five soldiers, said Sgt. 1st Class David Abrams, a military spokesman.

Separately, a suicide car bomber rammed into a U.S. military convoy in the northern city of Kirkuk, killing two civilians and wounding 13.

Attacks also flared in north-central Iraq.

In Tikrit, about 90 miles north of Baghdad, Lt. Col. Haitham Akram had just left his home and was getting into his car with his two sons when a bomb nearby went off, killing the three of them, police Lt. Qusay Mushaal said. The explosion set a nearby car ablaze, killing two young girls.

Around the city of Baqubah, east of Tikrit, a string of drive-by shootings killed a police lieutenant, three civilians and a Shiite Muslim student cleric.

Gunmen also killed three Iraqis driving a water truck to an Iraqi army base on a highway near Taji, north of Baghdad, police Lt. Abdul-Razaq Hayali said.

In Baghdad, gunmen opened fire on a car carrying Shiite workers, killing one and wounding two. Insurgents also killed a leader of a Shiite group and his driver in their car on a highway outside the southern city of Amarah, police said.