A homicide car bomber rammed into a crowded market in northern Iraq moments after a booby-trapped vehicle exploded Saturday, killing at least 11 people and injuring 65, police said.

The back-to-back blasts in the oil hub of Kirkuk contrasted with a lull in major violence in Baghdad as U.S. and Iraqi forces try to regain control from gangs and militias in the capital.

U.S. Secretary of State Condoleezza Ricemade an unannounced stop in Baghdad before heading for scheduled talks in Israel. She is the highest-level Washington official to visit Iraq since last month's announcement of a coordinated sweep against militant factions.

"If in fact militias decide to stand down and stop killing innocent Iraqis ... that can't be a bad thing," Rice told reporters traveling with her.

"But how the Iraqis use the breathing space that that might provide is what's really important," she said before meeting with Iraqi Prime Minister Nouri al-Maliki.

Some believe militants have made a tactical retreat to avoid the stepped up pressure and could regroup later. The attacks in Kirkuk, about 180 miles north of Baghdad, again showed the willingness of extremists to strike busy urban areas for maximum bloodshed.

Shops and a bus depot were filled with people when the first explosion occurred. Minutes later, a suicide car bomber slammed into the area in a mostly Kurdish district of the city, police said. The blasts also damaged about 20 shops.

At the city's main hospital, some of the injured were placed on floors after all beds and cots were filled. Restaurant owner Saman Ahmed was splashed with hot cooking oil as one of blasts hurled him onto the street. He lay on the sidewalk with burns and a broken leg as people fled amid burning cars and debris.

Kirkuk is a major oil center with a mixed population of Kurds and Sunni and Shiite Arabs. On Feb. 3, a series of car bombs in the city killed two people and injured 30.

Iraqi authorities said they foiled a potential suicide bomber near Karbala, about 50 miles south of Baghdad. A minivan came under fire after the driver failed to slowdown at a checkpoint, and then detonated the explosives and was killed in the blast, said Karbala police spokesman Rahman Mishawi. There were no other casualties.

In Baghdad, new checkpoints were set up around the city, creating long traffic jams as vehicles were thoroughly searched. Iraqi tanks pushed into districts that recently were ruled by roaming gunmen and militant groups.

On the outskirts of the city, Iraqi soldiers seized 50 Russian-made anti-aircraft missiles, said Brig. Gen. Qassim Moussawi. He declined to give more details because search teams were still in the area.

Violence in Baghdad has dropped off sharply since the military push began earlier this week. U.S. military planners, however, caution that any attempt to stabilize Baghdad could take months and it's likely militants will not leave without a fight.

"We are very optimistic," said U.S. Embassy spokesman Lou Fintor. Then he quickly added: "Things aren't going to change overnight."

Washington has pledged 21,500 additional troops for the operation, which is expected to reach a total of 90,000 U.S. and Iraqi forces.

"I would say that it is way too early to establish any trends," Lt. Col. Chris Garver, a U.S. military spokesman, said Friday. "We've just started to focus our operations. We have months to go to see if we are going to succeed or not."

Maj. Gen. Joseph Fil, commander of U.S. forces in Baghdad, attributed the reduction in violence not only to the increased security presence but also to an apparent decision by the militias and insurgents to lay low for a while.

"But make no mistake, we do not believe ... that's going to continue, and we do expect there are going to be some very rough, difficult days ahead," Fil said. "And this enemy knows how — they understand lethality and they have a thirst for blood like I have never seen anywhere before."