Later, the Iraqi government news agency, in a report carried on Arab satellite television, reported that two Iraqi women carried out a suicide attack on U.S. forces northwest of Baghdad. It appeared to refer to the same blast.
Al-Jazeera also carried video of two women vowing to commit suicide attacks. The station did not specify if the two were involved in the explosion, though it broadcast their statements immediately after citing the news agency report.
The attack occurred Thursday evening about 11 miles southwest of the Haditha Dam, Central Command said in a written statement. The site is northwest of Baghdad and about 80 miles east of the Syrian border, a spokesman said.
"A pregnant female stepped out of the vehicle and began screaming in fear," the statement said. "At this point the civilian vehicle exploded, killing three coalition force members who were approaching the vehicle and wounding two others." It said the woman and the driver also were killed.
Marine Brig. Gen. Vincent Brooks, U.S. Central Command deputy director of operations, said "these are not military actions. These are terrorist actions."
Al-Jazeera broadcast separate videotapes of two Iraqi women, each of whom stood in front of the Iraqi flag, right hand on the Quran placed on a table in front of her and left hand brandishing an automatic rifle.
A woman who identified herself as "martyrdom-seeker Nour Qaddour al-Shanbari" swore on the holy book of Islam "to defend Iraq ... and take revenge from the enemies of the (Islamic) nation, Americans, imperialists, Zionists" and Arabs who have submitted to the foreigners.
"We say to our leader and holy war comrade, the hero commander Saddam Hussein, that you have sisters that you and history will boast about," said the woman, who wore the red-checked keffiyeh, an Arab headscarf.
In a separate video, another woman, who identified herself as Wadad Jamil Jassem, stood in a similar pose.
"I have devoted myself for jihad (holy war) for the sake of God and against the American, British and Israeli infidels and to defend the soil of our precious and dear country," she said.
CBS News reports that while embedded reporters positioned with coalition troops say many Iraqi soldiers are surrendering, the enemy is still inflicting casualties on allied forces in the form of suicide attacks.
Jim Wilkinson, a spokesman at U.S. Central Command, said the incident showed the Iraqi leadership was using desperate measures to remain in power.
"The more desperate the regime gets, the more desperate their tactics become," Wilkinson said. "This is just the latest tragic example."
The Iraqi government has said suicide bombings will be a "routine military policy" and has promised more attacks.
U.S. officials have said the troops have a right to defend themselves against what they call "terrorist" tactics by the Iraqi regime.