Two soldiers and two civilians working with the U.S. military were killed Tuesday when a bomb detonated in an advisory council building in Baghdad’s Sadr City district.

One U.S. soldier and three Iraqi district council members were wounded in the blast, U.S. military officials said. The explosion happened around 9:30 a.m. in Thawra III, a southern sub-district of Sadr City.

A spokeswoman with the U.S. Embassy in Baghdad said the two U.S. civilian dead were employees of the State Department and the Department of Defense.

According to The Associated Press, an Iraqi Interior Ministry official said four Iraqi civilians were killed and 10 others wounded in the attack. It is common that U.S. and Iraqi officials have differing counts of dead and wounded civilians after incidents.

The military blamed the attack on what it calls "Special Groups" — Shiite militants who have splintered from larger militias. The U.S. military has repeatedly alleged that the Special Groups are trained and equipped by Iran. That country’s leaders have denied the allegation.

Lt. Col. Steve Stover, a U.S. spokesman in Baghdad, said three suspects have been arrested, though "it is too early to release any information on the suspects we have detained." At least one of the suspects was caught fleeing from the scene and tested positive for explosives residue, Stover said.

Tuesday’s bombing was described by another military official as "one cowardly act to halt progress, but it will only harden the determination of this council, the citizens of Sadr City, the Iraqi Army, and Coalition Forces."

According to Lt. Col. John Digiambatista, operations officer for 3rd Brigade, 4th Infantry Division, the bomb struck the fourth meeting of the nascent district council. U.S. forces routinely attend such meetings throughout Iraq.

"Special Groups are afraid of progress and afraid of empowering the people," he said.

The attack is the second time this week that insurgents targeted a joint U.S.-Iraqi government meeting.

On Monday, two soldiers and an interpreter were killed and three other soldiers were wounded in an ambush after a municipal council meeting in Madaen, a village near Salman Pak. The attacker was described as a former member of the council; he was killed in an exchange of fire after shooting at the Americans with an assault rifle.

U.S. troops in most parts of Iraq post heavy security around the buildings where they meet with Iraqi officials. Some of those meeting areas are swept by bomb-sniffing dogs and other measures. But responsibility for security both before and after the meetings falls on Iraqi security forces.

"Coalition forces and our Iraqi Security Force partners are committed to lasting security and stability throughout Baghdad," Col. Allen Batschelet, chief of staff for Multi-National Division-Baghdad and the 4th Infantry Division, said in a statement. "Today, two soldiers and those serving alongside them paid the ultimate sacrifice on behalf of the Iraqi and American people in pursuit of this goal. Our hearts and prayers are with them and their families."

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