Initial police reports indicated two policemen were killed and 14 others wounded on Thursday. At least 36 other Iraqi security members are listed as missing.
Police said fighters attacked a police convoy as it travelled between Diwaniya, 180km south of Baghdad, and the capital.
US forces sealed off the site of the ambush, near the Abu Ghraib area on Baghdad's western fringes. Police said some of the wounded were treated in hospital in Diwaniya.
The attack comes a day after fighters in the north dragged Iraqi soldiers off a bus and shot 12 of them dead, and suggests the country's 22-month-long anti-US campaign is far from over.
At least a dozen civilians were also killed in Thursday's bloodshed, the worst this week.
Three Iraqi soldiers were also killed and three wounded in a bomb attack on Thursday morning in Yathrib, 75km north of Baghdad.
After a two-day lull, Thursday
witnessed a surge of attacks
"A man was arrested at the scene of the attack but was freed due to lack of evidence," Captain Amjad Saad said.
Elsewhere, a soldier and a woman were killed in a bomb blast targeting an army convoy at Shurqat, 300km north of Baghdad, a police officer said, explaining that the woman was driving behind the convoy.
And in a rare case of civilians fighting back, villagers killed five fighters who attacked them for taking part in the elections, police said on Thursday.
Earlier, two Iraqi employees of a US military base were shot dead and four of his colleagues wounded while on their way to work in Baquba, northeast of Baghdad, a medical source said.
Tal Afar in the north has been the
scene of violence for months
One of the wounded men, Raid Rizuqi, said he and his friends were driving to work when fighters opened fire from another car.
Baquba's general hospital confirmed they received one corpse riddled with bullets.
Also on Thursday, an Iraqi soldier was killed by assailants as he was leaving his home in Baghdad, officials said.
In another incident, the governor of al-Anbar province, a stronghold for fighters west of the capital, escaped assassination on Thursday when a roadside bomb exploded near his car in Ramadi.
In a separate development, Aljazeera learned that an unknown number of US soldiers were killed and wounded when a house used as a US military headquarters was destroyed in al-Qaim city in western Baghdad.
Witnesses reported other US troops firing back, hitting several civilian bystanders.
The latest deaths brought the
overall toll of US troops to 1441
In northern Iraq, a mortar attack on a US position fell short and killed two civilians and wounded six in Tal Afar, the US military said.
"The insurgent minority attempted to fire mortar rounds at the Tal Afar Castle, instead missing and killing and wounding innocent Iraqis," the military said in a statement.
Tal Afar, west of the northern city of Mosul, has been the scene of violence for months between US forces and anti-US fighters.
On Wednesday two US marines were killed in action in Iraq's western province of al-Anbar, the US military said.
Anbar is a huge, predominantly Sunni area which stretches westwards from the outskirts of Baghdad to the Saudi, Jordanian and Syrian borders, and includes the towns of Falluja and Ramadi.
The marines' death raised the overall toll for US soldiers killed in Iraq to 1441 since the US-led invasion of March 2003, according to Pentagon figures.