BAGHDAD, (AP) – U.S. forces backed by airstrikes raided Sadr City, Baghdad’s main Shiite district, killing 49 militants on Sunday as they targeted a militia leader accused in high-profile kidnappings, the military said. Iraqi officials said women and children were among the dead.

The Iraqi reports followed other recent claims of civilian deaths as a result of U.S. military action or shootings by private Western security teams protecting American diplomats and aid groups. The military said it was not know of any civilians killed.

Tensions also rose in northern Iraq after separatist Kurdish rebels ambushed a military unit near Turkey’s border with Iraq, killing at least 12 soldiers. Turkey’s government has threatened to take action against the rebels based in northern Iraq if the U.S.-led coalition in Iraq does not stop the Kurdish attacks on Turkish forces.

Hours after the ambush, an Iraqi army officer from the border guard forces, Col. Hussein Rashid, said Turkish forces fired about 15 artillery shells toward Kurdish villages in the border area in northern Iraq. But there were no casualties.

In Sadr City, the U.S. military said “an estimated 49 criminals” were killed in three separate engagements during a raid targeting a suspected rogue Shiite militia leader specializing in kidnapping operations for which he sought funding from Iran.

U.S. troops returned fire after coming under sustained attack from automatic weapons and rocket-propelled grenades from nearby buildings as they began to raid a series of buildings in the district, according to a statement, which added that some 33 militants were killed in the firefight. Ground forces then called in airstrikes, which killed some six militants.

The U.S. troops were then attacked by a roadside bomb and continued heavy fire as they left the area, killing another 10 combatants in subsequent clashes.

“All total, coalition forces estimate that 49 criminals were killed in three separate engagements during this operation. Ground forces reported they were unaware of any innocent civilians being killed as a result of this operation,” the military said in the updated statement.

Iraqi police and hospital officials put the death toll at least 13 and said a woman and three children were among the dead from the pre-dawn raid in the sprawling district. They said 52 people were injured.

Associated Press photos showed the bodies of two toddlers, one with a gouged face, swaddled in blankets on the floor of the morgue. Relatives said they were killed when helicopter gunfire hit their house as they slept. Their shirts were pulled up, exposing their abdomens. A diaper showed above the waistband of the shorts of one of the boys.

Several houses, cars and shops were damaged in the fighting, which witnesses said lasted two hours.

Iraqis have routinely claimed civilians were killed as U.S.-led forces stepped up raids to try to root out extremists in Sadr City and other Shiite strongholds as part of an 8-month-old security operation to quell sectarian violence.

But the reported death toll in Sunday’s strike was among the largest.

On Aug. 8, the U.S. military said 32 suspected militants were killed and 12 captured in an operation targeting a ring believed to be smuggling armor-piercing roadside bombs from Iran. Iraqi police and witnesses claimed nine civilians, including two women, were killed in that raid.

The sweeps into Sadr City have sent a strong message that U.S. forces plan no letup on suspected Shiite militia cells despite risks of upsetting the Shiite-led government of Prime Minister Nouri al-Maliki and its efforts at closer cooperation with Shiite heavyweight Iran.

An Iraqi military spokesman, Brig. Gen. Qassim al-Moussawi, said the government would ask the military for an explanation about Sunday’s raid and stressed the need to avoid civilian deaths everywhere.

The government has had mixed reactions to the raids and airstrikes, particularly when they target Sunni extremists.

U.S. troops backed by attack aircraft also killed 19 suspected insurgents and 15 civilians, including nine children, in an operation Oct. 11 targeting al-Qaeda in Iraq leaders northwest of Baghdad.

In that case, al-Maliki’s government said the killings of the 15 women and children were a “sorrowful matter,” but added that civilian deaths are unavoidable in the fight against al-Qaeda.

Relatives gathered at Sadr City’s Imam Ali hospital as the emergency room was overwhelmed with bloodied victims and the dead were placed in caskets covered by Iraqi flags.

An initial military statement e-mailed to The Associated Press said the raids were targeting “criminals believed to be responsible for the kidnapping of coalition soldiers in November 2006 and May 2007.”

However a later release said only that U.S. troops, acting on intelligence, raided a number of buildings in an operation targeting a rogue Shiite militia leader specializing in Iranian-funded kidnappings.

The military said it was targeting a member of a breakaway faction of the Mahdi Army militia that is nominally loyal to Muqtada al-Sadr. The anti-American cleric has called on his fighters to stand down.

At the Imam Ali hospital, a local resident who goes by the name Abu Fatmah said his neighbor’s 14-year-old son, Saif Alwan, was killed while sleeping on the roof. Fatmah said many of the casualties were people sleeping on the roof to seek relief from the hot weather and lack of electricity.

“Saif was killed by an airstrike and what is his guilt? Is he from the Mahdi Army? He is a poor student,” Abu Fatmah said.

An uncle of 2-year-old Ali Hamid said the boy was killed and his parents seriously wounded when heavy gunfire from a helicopter struck the wall and windows of their house as they slept indoors.

APTN video showed a U.S. helicopter flying over the area while black smoke rose into the sky.

Other footage showed three bloodied boys sitting on hospital tables and an elderly man being treated for a head wound.

Mourners tied wooden coffins onto the tops of minivans with the plume of smoking rising in the background.