Three civilian workers killed in Iraq
Attackers dressed as Iraqi police officers
Members of the Iraqi Governing Council sign their country's interim constitution.
CNN's Ben Wedeman on a rocket attack in Baghdad before the signing.
The U.S. administrator for Iraq says ending the occupation is key for Iraqis and Americans.
BAGHDAD, Iraq (CNN) -- Coalition officials are questioning six suspects on Wednesday believed to have killed three civilian workers, Iraqi police said, adding that five of the attackers were dressed as Iraqi police officers.
Two U.S. civilians and an Iraqi translator working with the U.S.-led coalition were killed near Karbala in Iraq on Tuesday night.
The victims were driving from a women's rights center in Karbala when they were ambushed in Abi Gharaq, about a mile away, Iraqi police said.
The six suspects drove a Nissan pickup truck, police said. It is not clear if the suspected attackers were members of the Iraqi police force or wearing the uniforms as a disguise.
In other violence Tuesday night, a firefight in southern Iraq near Nasiriya, between Iraqi police and an Iraqi independent militia, killed four policemen and wounded four others, a coalition official said.
Italian troops are based near Nasiriya. The Italians responded and were involved in quelling the incident, officials said.
In Baghdad, six rocket-propelled grenades were fired near the coalition's headquarters Wednesday morning, coalition officials said. No injuries were reported.
The blasts could be heard around 6:45 a.m. (10:45 p.m. Tuesday ET). The RPGs were fired at a communications antenna near the entrance to the Baghdad Forum.
Also Wednesday, the Coalition Joint Task Force said U.S. forces in Ejba in northern Iraq accidentally killed an Iraqi citizen and wounded another Monday after firing back at hostile forces.
Task Force Olympia met Tuesday with the family and local leaders to discuss the incident, which is under investigation.
Meanwhile, doctors on Wednesday will autopsy the body of Palestinian militant leader Abu Abbas, who died in U.S. custody in Iraq on Monday. The Pentagon said Abbas apparently died of natural causes. (Full story)
U.S. Special Forces captured Abbas April 14, 2003 on the outskirts of Baghdad. Abbas tried to flee to Syria, but was turned away at the border and was captured about 50 miles west of Baghdad, a Palestinian source said.
Abbas was the the head of the Palestine Liberation Front, the offshoot of the Palestinian Liberation Organization. In 1985, the group hijacked the Achille Lauro, an Italian cruise ship. The hijackers sparked outrage in the Western world when they killed a disabled American Jew, Leon Klinghoffer, 69, and dumped his body and wheelchair overboard.
Ilsa and Lisa Klinghoffer said Tuesday they have worked since their father's death to have Abbas tried in court.
"Now, with his death, justice will be denied," they said in a statement. "The one consolation for us is that Abu Abbas died in captivity, not as a free man."
Other developmentsThe Coalition Joint Task Force said U.S. forces in Ejba accidentally killed an Iraqi citizen and wounded another on Monday after responding to hostile forces. Task Force Olympia met Tuesday with the family and local leaders to discuss the incident, which is under investigation.