BAGHDAD, Iraq (AP) – Drive-by shootings, roadside bombings and sectarian killings left nearly 20 Iraqis dead in Baghdad Friday. American and Iraqi troops swept the oil-rich region of Kirkuk for suspected insurgents and captured dozens.

Drive-by gunmen killed three policemen in west Baghdad and three power station workers headed to their jobs in Taji, just north of the capital, police said.

In south Baghdad’s Saydiyah district, gunmen killed four employees of a pastry shop, police said. Nearby, a roadside bomb killed a policeman.

Retaliatory killings between Shiite and Sunni Muslims have become increasingly common in the capital since the Feb. 22 bombing of an important Shiite shrine that unleashed the continuing rash of sectarian murders. Baghdad police said they discovered 13 bodies, blindfolded and shot, on Friday in the Binok, Kazimiyah and Sadr City neighborhoods.

Meanwhile, soldiers of the 1st Brigade Combat Team, 101st Airborne Division joined Iraqi troops in a sweep of five villages outside the city of Kirkuk, 290 kilometers (180 miles) north of Baghdad. Forty suspected insurgents were picked up in Hawija, police said. A day earlier, the U.S. military spokesman in Iraq asserted that major violence is largely confined to just three of the country’s 18 provinces, where fighting raged on Thursday with at least 58 people killed in execution-style slayings, bombings and gunbattles.

For the third straight day Thursday, Sunni insurgents hit a major police and jail facility, this time with a suicide car bombing that killed 25 in central Baghdad. The attacker detonated his explosives at the entrance to the Interior Ministry Major Crimes unit in the Karradah district, killing 10 civilians and 15 policemen, authorities said. As insurgent forces raised the stakes with the attacks, the U.S. military announced late Thursday that it was in the second day of an operation with Iraqi soldiers “to disrupt anti-Iraqi forces and to find and destroy terrorist caches in the Abu Ghraib area west of Baghdad.”

The military statement said 1,400 personnel were involved in the operation, termed Northern Lights, and had captured “two persons of high-value interest and 16 suspected terrorists.” Two large weapons caches also were discovered, the military said.

Abu Ghraib, also the site of the infamous prison, is where U.S. and British forces stormed a house Thursday morning and freed three Christian peace activists held hostage since Nov. 26.

The Interior Ministry unit that was targeted Thursday investigates major crimes, and its jail held about 20 suspected insurgents, police Lt. Col. Falah al-Mohammadawi said. The ministry is a predominantly Shiite department and is heavily infiltrated by members of various Shiite militias.

In a rundown of recent military activity, Maj. Gen. Rick Lynch, the U.S. military spokesman, told reporters Thursday that most Iraqi violence was focused in three central provinces, including Baghdad.

“There is not widespread violence across Iraq. There is not. Seventy-five percent of the attacks still take place in Baghdad, al-Anbar or Salaheddin (provinces). And in the other 15 provinces, they all averaged less than six attacks a day, and 12 of those provinces averaged less than two attacks a day.” He said attacks nationwide were averaging 75 a day, a level that has been generally sustained since last August.

The three provinces he cited, however, are home to about 9 million people, according to the Iraqi Ministry of Planning and Development, a third of the country’s population of 27 million.

Lynch’s list omitted Diyala province, which stretches north and east of Baghdad to the Iranian border and is home to nearly 1.5 million people. It was the scene Tuesday of the first of the series of attacks on police facilities, when 100 insurgents stormed a jail and freed 33 prisoners, 18 of them their own men captured two days earlier. That attack killed 20 police and wrecked the jail, police station and courthouse in Muqdadiyah, 60 miles northeast of Baghdad. Ten insurgents were killed.

As Iraqi soldiers and police have begun patrolling more territory, U.S. forces have become less visible in many areas in the country and less easy to target. Also, the nature of the violence in the country has shifted from assaults on American troops to battles rooted in sectarian conflict between Sunni and Shiite Muslims.

Well over 1,000 people have died violently in Iraq, mainly in and around Baghdad, since the shrine bombing in Samarra, a city north of Baghdad in Salaheddin province. The sectarian-rooted deaths since then have been running at dozens a day. The bodies of hundreds of victims have been dumped after being shot execution-style, hands bound and bearing signs of torture.

Lynch acknowledged a spike in “ethnic-sectarian incidents,” saying there were 75 percent more civilian casualties during March 11-17 than in the previous week. In Baghdad alone, he said, the U.S. command recorded 58 incidents involving 134 dead during that period.

Besides the attack on the police facility Thursday, 33 other deaths were reported, including 15 more bodies found scattered through Baghdad and Fallujah, a former insurgent stronghold in Anbar province, west of the capital.

A second car bomb hit a market area outside a Shiite mosque in the mixed Shiite-Sunni neighborhood of Shurta in southwest Baghdad. At least six people were killed and more than 20 wounded, many of them children, police said.

Roadside bombs targeting police patrols killed two policemen and two bystanders in Baghdad and at least one policeman in Iskandariyah, 30 miles (50 kilometers) south of the capital. Police said dozens were wounded. Another roadside bomb killed a Danish soldier and wounded another just north of Basra in southern Iraq, authorities said.

Two more policemen were killed and two were wounded when gunmen ambushed their convoy in north Baghdad, an attack that police described as an aborted attempt to free detainees who were being transferred to the northern city of Mosul. Elsewhere in the capital, two police were killed in gunbattles with insurgents, and two civilians, a private contractor and power plant employee, were gunned down in drive-by shootings.