Updated

A wave of early morning explosions in and around the Iraqi capital killed 16 people Sunday and for the third time this month, Iraqi security forces were the main target.

Insurgents have been hammering the security forces in an attempt to undermine Iraqis' confidence in the ability of their police and military to take over from American forces scheduled to leave the country by the end of this year.

At least nine of those killed were police officers, underscoring the risks of the job.

"The aim of these attacks is to send a message to the locals: 'If the security people cannot protect themselves then how can they protect you?'" said Iraqi police Capt. Majid Mohammed Amin, who joined the police in 2000 and has since survived two roadside bombings.

The worst single attack took place near the city of Taji, 12 miles (20 kilometers) northwest of Baghdad. It was an almost textbook insurgent ambush. First a roadside bomb targeting an American military convoy exploded. When police arrived on the scene, a suicide bomber walked into the crowd and blew himself up, police and hospital officials said.

Seven police and three civilians were killed and 19 people, including 15 policemen, were injured, the officials said.

Earlier, at least 10 bombs exploded around the capital at the start of the workweek.

At about 7 a.m. a car bomb in a parking lot in eastern Baghdad's Sadr City neighborhood exploded, injuring five people and damaging nearby cars.

"We woke up to a big blast nearby and the glass windows in front of the house were smashed. My young brother was injured by glass," said Namiq Khazal, a 30-year-old Sadr City resident who lives a short distance from where one of the blasts went off.

Minutes later, also in Sadr City, a bomb hidden in a pile of garbage exploded, killing one person and wounding five more. Then five minutes later another roadside bomb, this time targeting a police patrol, exploded; three policemen and four bystanders were injured in that blast.

In the southwestern neighborhood of Bayaa, five explosions went off in rapid succession, killing five people, including two policemen, and injuring another 15, including six policemen, police and hospital officials said.

In the upscale Karradah neighborhood, two roadside bombs injured 14 people, including six policemen, police and hospital officials said.

The officials all spoke on condition of anonymity because they were not authorized to speak to the media.

It was the third day this month in which security personnel suffered serious casualties. Last week, 27 people were killed outside a police station in the northern city of Kirkuk, and earlier this month 20 police officers in the southern city of Hillah died when a suicide bomber plowed his vehicle into a police compound.

Security officials have also been targeted in an almost daily barrage of assassination attempts involving sticky bombs attached to the undercarriage of vehicles, roadside bombs and gunmen using weapons fixed with silencers.

About 46,000 American troops remain in bases around Iraq, and they are slated to leave the country by Dec. 31. But as the deadline approaches, many Iraqis are worried about the ability of their own forces to protect the country from the ever-present threat of bombs and shootings.

In the northern city of Kirkuk on Sunday, police found the body of a man believed to be in his late 20s, said the neighborhood police chief, Col. Anwar Qadir. The man's hands were tied behind his back and he was killed execution-style with a bullet to the back of his head.

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Associated Press writer Mazin Yahya in Baghdad and Yahya Barzanji in Sulaimaniyah contributed to this report.