A suicide car bomber attacked the main checkpoint to Baghdad's international airport on Wednesday, wounding 15 Iraqis, the U.S. military said. Other violence claimed the lives of two police officers and four civilians, including three children, officials said.

The car bomb exploded next to a security checkpoint where Iraqi workers were waiting in long lines in their vehicles to enter the sprawling airport grounds.

Hussein Muhsen, an aircraft engineer with Iraqi Airways, described a loud blast followed by a mountain of dust rising in the air. Blood and human limbs splattered down on cars, Muhsen said.

U.S. forces said insurgents opened fire after the attack. Witnesses said American troops also fired.

The airport road has been one of the most frequent scenes of insurgent attacks since the U.S. invasion in 2003.

In southern Baghdad, three children -- ages 12, 10 and 8 -- and their uncle were killed by mortar fire as they played outside their home, the Associated Press reported, citing a hospital official and a relative. It also reported the deaths of two policemen in drive-by shootings in the Amil district of western Baghdad and in the northern city of Samarra.

Iraq has experienced daily bombings for months, and Wednesday was one of the first days in weeks in which no fatalities other than the bomber were immediately reported from such attacks. Bruska Noori Shaways, secretary general of Iraq's Defense Ministry, said a reduction in attacks in Baghdad in the past three or four days might be linked to an ongoing Iraqi-led mission, Operation Lightning, that has increased checkpoints on roads into the capital and at some points in the city.

Iraqi authorities have detained about 680 people so far in the operation but have released all but 95 for lack of evidence warranting prosecution, Shaways said.

The U.S. military said Wednesday that it had arrested a former intelligence operative from Saddam Hussein's secret service who was suspected of financing several insurgent groups in western Baghdad.

Bombings and other violence have soared since an elected government led by Iraq's Shiite Muslim majority took office on April 28. Iraqi and U.S. officials say they believe the daily suicide bombings in particular are organized by foreign fighters trying to drive out U.S. troops and undermine the new government.

Early Thursday, two car bombs exploded near the northern city of Kirkuk, killing 10 people and wounding at least 34. The first, south of the city in the town of Tuz, exploded near a restaurant and targeted vehicles belonging to the Kurdish Democratic Party. Nine people were killed and 23 wounded, according to Col. Abbas Mohammed Amin, the police chief. A second blast shook the entrance to the Northern Oil Co., killing a 5-year-old and wounding about 11 people, said Maj. Gen. Torhan Yousif, chief of the Kirkuk police.

Attacks since April 28 have killed more than 700 Iraqis, according to a tally by the Associated Press, which also said there were about 100 suicide attacks in May.

In Washington, the State Department announced that the United States and the European Union would co-host an international conference in Brussels on June 22 to help the Iraq coordinate its political, economic and security goals.

With less than three months until a new constitution is due and seven months until planned elections for a permanent government, the United States and its partners in Iraq are increasingly concerned about losing momentum during the transition. The Bush administration also wants to prod nations that have not followed through on aid pledges totaling billions of dollars, in part because of Iraq's security situation. The conference will attempt to match donor nations with specific projects, U.S. officials said.

Foreign Minister Hoshyar Zebari said the new government, which took three months to assemble after the January elections, would outline its priorities during this phase of the transition. "We think that this will be a very important event to reengage the international community and Iraq to help us overcome the current difficulties," Zebari said after talks in Washington with Secretary of State Condoleezza Rice. "We are going through a very important period in the entire political transition."

Rice will lead the U.S. delegation at the Brussels conference, which was requested by Iraq. More than 80 nations and international aid organizations are expected to attend, the State Department said.

Despite the heightened focus on strengthening Iraq's governmental institutions and reviving stalled reconstruction by year's end, the Bush administration acknowledged Wednesday that the military transition was still unpredictable.

"As Iraqis take more and more of a role and a responsibility, the coalition will change its presence or its nature," State Department spokesman Richard A. Boucher said. "But that's not a completely predictable process because you're dealing with a real enemy out there, a real danger in form of the insurgency and the terrorists that are there."

Staff writer Robin Wright in Washington and special correspondent Marwan Ani in Kirkuk contributed to this report.

An Iraqi injured in a suicide car bombing leaves Baghdad's Yarmouk Hospital. More than 700 Iraqis have been killed in mounting violence since April 28.