BAGHDAD, Dec. 5 — Car bombs in Baghdad and three northern Iraqi cities killed at least 23 people and injured more than 40 others today as Defense Secretary Robert M. Gates arrived for an unannounced visit with senior Iraqi officials.
The car bombings, including a particularly deadly suicide car bomb attack on a crowded street in eastern Baghdad that killed more than a dozen people, served as a vicious reminder that the months-long decline in daily violence was not a sure harbinger of any kind of lasting peace.
Indeed, the four car bombs — the first of which detonated in the northern city of Mosul shortly before Mr. Gates' plane arrived there early today, seemed timed to coincide with his visit. None of the bombings, however, occurred anywhere close to the defense secretary or his entourage.
In Baghdad, Mr. Gates met with Prime Minister Nuri Kamal al-Maliki and other top government officials to press them to use the recent nationwide lull in daily violence and sectarian killings to pass key legislation and improve government services.
The first three car bombings occurred in Mosul, Kirkuk and Baquba — three cities north of Baghdad where Al Qaeda-linked insurgents have battled Iraqi and American forces for control.
The most deadly attack today by far, though, happened just before 5 p.m., in Baghdad's religiously mixed Shiite Karrada district, across the Tigris River from the fortified Green Zone where Mr. Gates was holding meetings.
The suicide car bomber detonated near the Abdul Rasul Ali mosque, a Shiite shrine, and destroyed a public bus filled with people; shortly afterward, eight to 10 incinerated bodies of passengers were visible in the smoking hull of the vehicle.
The blast also killed several street vendors; human remains, including that of a motorcyclist ripped in half, were scattered over a hundred-yard area, according to a New York Times employee who witnessed the aftermath.
In Mosul, a car bomb that apparently targeted an Iraqi police patrol exploded around 9 a.m., shortly before Mr. Gates' arrival, killing one person and injuring seven others, a police officer in Mosul said.
In Baquba, a suicide bomber driving a car laden with explosives detonated at the entrance to a bus station, killing five people and wounding 20 others, a local police officer said.
And in Kirkuk, an oil-rich city in Iraq's north, a bomb left in a parked car near the city's southern gate killed two people and injured 10 others, Iraqi police there reported.
Also today, the military announced that two American soldiers were killed in Salahaddin Province, north of Baghdad.
In Kut, a mostly Shiite city south of Baghdad near the Iranian border, gunmen killed a prominent Shiite tribal leader, Abbas Challab, according to Iraqi security forces. In an unrelated arrest, also in Kut, an Iraqi special operations force arrested a Sunni Arab man, Dhiab al-Dainie, whom they said is a senior Qaeda leader.