A parked car bomb went off near a police patrol Friday afternoon in a central Baghdad shopping district, killing four people, including two policemen, as Iraq's Sunnis began marking the Eid al-Fitr holiday that ends the Muslim holy month of Ramadan.

In northern Iraq, a bomb planted near a children's playground killed one person and injured 17 others, police said.

The U.S. military, meanwhile, said it was working with local Iraqi officials and tribal officials to investigate the killings of 15 civilians — six women and nine children — as well as 19 suspected insurgents Thursday in a U.S. ground and air assault targeting Al Qaeda in Iraq northwest of Baghdad.

The blast in Baghdad also wounded 15 people, most civilians, damaged several shops and two nearby cars, a police officer said speaking on condition of anonymity because he was not allowed to release the information.

The officer, citing eyewitnesses, said the suspected bomber had parked his car by some clothing stores, pretending to go shopping during the busy start of the holiday. The attacker managed to flee, the officer added.

In northern Iraq, a bomb planted among toys in a cart left near a children's playground in the religiously mixed city of Tuz Khormato north of Baghdad, killing one civilian and wounding 17, including five children, police Col. Abbas Mohammed said.

The U.S. military operation near the man-made Lake Tharthar, about 50 miles northwest of the capital, inflicted one of the heaviest civilian death tolls in the offensive against the terror network in recent months.

Nineteen insurgents and 15 civilians, including nine children, died in the raid, the military said.

The military statement said ground and air assault troops acted on intelligence reports about an Al Qaeda meeting at an initial location, then pursued suspected insurgents to another area. Two suspected Al Qaeda members, a woman and three children were also wounded, said the military, expressing regret "that civilians are hurt or killed while coalition forces search to rid Iraq of terrorism."

In a new statement Friday, the military said the Tharthar deaths were under investigation and that U.S. forces "take every precaution to protect innocent civilians and only engage hostile threats."

The Al Qaeda network had announced stepped-up attacks during Ramadan, after increased pressure by American forces since the full contingent of additional U.S. troops arrived June 15.

But al-Maliki recently confronted top American commander Gen. David Petraeus about what he sees as overly aggressive U.S. tactics that harm the innocent, according to Iraqi officials.

On Oct. 5, a pre-dawn U.S. raid on Khalis, a Shiite city north of Baghdad, killed 25 people when U.S. troops called in airstrikes after meeting a fierce barrage while hunting suspected smugglers of arms from Iran to Baghdad. Village leaders said the victims included civilians, but the military insisted the 25 killed were militants.

Tensions were also rising in Iraq's northern Kurdish region amid saber-rattling from neighboring Turkey, whose Prime Minister Recep Tayyip Erdogan said Friday that his country would be ready to pay the price of any Iraq campaign if it decides to stage a cross-border offensive against Kurdish rebels sheltering in Iraq.

The development came in the wake of the killing of 13 Turkish soldiers last Sunday in a clash with rebels of the Kurdistan Workers Party, or PKK, in the country's southeast province of Sirnak bordering Iraq.

Turkey's parliament is set to debate more next week whether to approve sending troops to Iraq. Such a decision is likely to strain Turkish ties with the United States and Iraq.

Petraeus warned Thursday that Turkey's threatened incursion could harm the flow of supplies for U.S. troops and damage the Kurdish economy in the north. Iraqi Kurdistan, a region of relative calm and a strong U.S.-ally, could become another fault line if Turkey makes good on the threat to stage an incursion.

Turkey claims the rebels, who have fought Ankara since 1984, use Iraqi Kurdish territory as a safe haven. Iraqi and Kurdish authorities reject the claim.