A suicide bomber rammed his car into a police patrol Thursday in northern Iraq, killing six people and wounding more than 20 others. Despite the violence in Iraq, a U.S. military official says the number of attacks and casualties due to roadside bombs is at its lowest level in two years. Deborah Block has more from the northern Iraqi city of Irbil.

The car bomb exploded in the city of Kirkuk north of Baghdad. The target was a six-car convoy carrying a senior Kurdish police officer, Khattab Omar, who heads the quick response force. He survived, but other officers did not. Many of the wounded are children who were walking to a nearby school. Kirkuk policeman Tahir Salah-Eddin.

He says a suicide bomber detonated his car next to Kirkuk police department vehicles, killing three policemen and wounding civilians.

The U.S.military on Thursday announced that an American soldier was killed a day earlier in an explosion in Diyala province. Four more soldiers were wounded in the blast.

In Baghdad, U.S. Major General James Simmons said the number of attacks from roadside bombs is at its lowest in two years.

Compared to the more than 3,200 incidents last March, some 1,500 roadside bombs either exploded or were found in October. Simmons says this is because of tips about weapons caches from Iraqi citizens and also Iran's commitment to stem the flow of weapons and explosives into Iraq.

"We have found weapons that we believe are associated with Iran, in some of the caches we've picked up. But most appear to have been in Iraq for months. We have not seen any recent evidence that weapons continue to come across the border into Iraq," he said.

Iranian officials have denied smuggling weapons to Shiite extremists in Iraq and, last August, promised Iraqi officials they would work to stem the flow of weapons.

U.S. authorities say a deadly roadside bomb they believe comes from Iran has often been used by Shiite militants.

They also say that kind of bomb was used Wednesday against an American military vehicle near the entrance of the Green Zone in Baghdad. One American soldier and two Iraqi civilians were killed in the blast. It is the first major attack against a U.S. military vehicle in that area over the past few months.