Baghdad (AP): Mortar shells slammed into a residential area north of Baghdad, killing at least four people and wounding 30, most children playing outside, officials said on Sunday.

The shelling occurred as clashes broke out in Shiite areas late Saturday despite a truce reached last week by Shiite politicians and followers of anti-U.S. cleric Muqtada al-Sadr.

Bandaged girls and boys with bloodstained clothes cried as they were packed two to a bed at a hospital in Sadr City, a stronghold of al-Sadr's Mahdi Army militia where most of the recent fighting has occurred.

At least three mortar rounds struck a house, an open area and a street where boys were playing soccer in the Maamil neighborhood on Baghdad's northeastern outskirts, witnesses said.

Those killed included a man and three children, according to police and hospital officials who also said at least 30 people were wounded.

Associated Press photos showed men holding two dead babies bundled in blankets. Relatives identified them as 1-year-old Zahra Kadhim and 2-year-old Abbas Nadim.

Sporadic gunbattles also occurred in some areas of Sadr City, but no casualties were reported, police said.

Fighting between Shiite militiamen and U.S.-Iraqi forces has ebbed but occasional clashes continue to break out, casting doubt on the durability of the truce deal reached last Monday.

The U.S. military said Iraqi soldiers captured a ``special groups'' cell leader blamed for coordinating roadside bombings and rocket attacks against U.S.-Iraqi forces in an operation in Husseiniyah, about 30 kilometers (20 miles) north of Baghdad.

The term ``special groups'' refers to Shiite militia fighters who are ignoring al-Sadr's cease-fire order.

The military did not immediately respond to a request for comment about the violence in Maamil and it was not clear if it was connected to the operation in nearby Husseiniyah.

American soldiers also killed two ``special groups'' militants after coming under attack by a roadside bomb and small-arms fire in the northern Shiite neighborhood of Kazimiyah, according to a separate military statement.

The skirmishes in Baghdad came as the Iraqi government has shifted its attention to an offensive aimed at clearing Sunni insurgents from the northern city of Mosul.

The military said 15 suspects have been detained in raids targeting al-Qaida in Iraq so far on Saturday and Sunday, including eight in Mosul _ six who were linked to a militant leader in the city and two during an operation to disrupt a planned suicide car bombing attack. Iraqi officials say around 1,000 people have been detained in the sweep since May 10.

Iraq's leaders presented the crackdown as a success so far in depriving the terror network of what has been its most prominent urban stronghold since it lost hold of cities in Iraq's western Anbar province.

But many of the fighters have fled to nearby areas, where troops are hunting for them, Iraqi officials said, raising the concern they can regroup elsewhere, as has often happened in the past.

Separately, the top U.S. commander in Baghdad revealed that an American soldier had admitted to using a Quran, the Islamic holy book, for target practice, according to CNN.

The network reported that the staff sergeant, whose name was not released, was a sniper section leader assigned to the headquarters of the 64th Armored Regiment. It said he shot at the Quran on May 9 and the holy book used in the incident was discovered two days later.

Maj. Gen. Jeffery Hammond issued a formal apology Saturday to tribal leaders in Radwaniyah, west of the capital, for the incident.

``I come before you here seeking your forgiveness,'' Hammond said at the apology ceremony that was broadcast on CNN. ``In the most humble manner I look in your eyes today and I say please forgive me and my soldiers.''

The commander also read a letter of apology by the shooter, and another military official kissed a Quran and presented it to the tribal leaders.

A military investigation found the shooter guilty and relieved him of duty, CNN said.

U.S. House Speaker Nancy Pelosi, meanwhile, said she ``made clear that the war must be brought to an end'' as she met with top Iraqi and U.S. officials during a visit to Baghdad on Saturday.

``It has already taken far too many American and Iraqi lives, it has cost far too much in money and the reputation of the United States, and it has drained far too much from the capability of our military,'' she said in a statement.

The California Democrat led a bipartisan delegation to Iraq, where they met with Iraqi Prime Minister Nouri al-Maliki, parliamentary speaker Mahmoud al-Mashhadani, U.S. Ambassador Ryan Crocker and Gen. David Petraeus, the top American commander in Iraq.

She also said she was assured that upcoming provincial elections will promote national reconciliation.

``The Iraqi officials said that provincial elections would be held this year and that they would be transparent, inclusive, and a step toward national reconciliation. I hope this will be the case,'' she said.