"Last night approximately 18 km (11 miles) from Haditha dam in Iraq, a civilian vehicle approached a coalition checkpoint. A pregnant female stepped out of the vehicle and began screaming in fear," a statement from war headquarters in Qatar said on Friday.
"At this point the civilian vehicle exploded, killing three coalition force members who were approaching the vehicle and wounding two others. The pregnant female and the driver of the vehicle were also killed in the attack."
The nationality of the troops was unclear. The incident was northwest of Baghdad in an area where special forces are present but where US-led forces are thin on the ground.
"We are treating it as another desperate act of a dying regime that knows they're in trouble. It's unconventional warfare that continues to be used by the Iraqi regime," US Marine Captain Stewart Upton told Reuters.
Asked if it was considered a suicide attack, he said: "Yes."
Four US soldiers died in a suicide car bombing at another checkpoint on Saturday, putting invading forces across Iraq on edge. Iraq promised more suicide attacks would follow.
A number of Iraqi civilians have been shot by nervous troops at checkpoints, when vehicles have failed to stop.
US officials said earlier this week that they had seized the Haditha dam and were impeding Iraqi movements along the road north from Baghdad to President Saddam Hussein's home town of Tikrit. The road runs to the east of the dam.
Associated Press adds: Elsewhere in Baghdad, US troops battled through heavy gunfire and loyalist ambushes Thursday, as looting surged and buildings were set ablaze across the ancient city.
Massive explosions rocked the Old Palace presidential compound on a bend in the Tigris River at dusk, apparently Iraqi remnants firing on US positions within the grounds. US Army troops occupying the palace compound appeared to return fire with tank cannons.
With armed Iraqis in civilian clothes crouching behind bushes and some US positions taking heavy fire, US units slogged through firefights with loyalists to President Saddam Hussein in and around the city.
One US Marine company fought a firefight for several hours into the morning Thursday, with both light and heavy weapons, as it pushed its way through city streets.
Armed Iraqis appeared to hold much of northwest Baghdad, which was a no man's land with all shops closed and no US military presence except at one intersection.
In other parts of the city, tens of thousands of people, young and old, men and women roamed the city in the second round of looting since Wednesday. American forces made little or no effort to stop them as they carried off TV sets, refrigerators, carpets and other items.
At As-Salaam presidential palace for foreign dignitaries, looters stripped the rooms of its faux French provincial furniture. Iraqis looted the bedrooms, with their 8-meter (25-feet) ceilings, of blankets and carpets.
Iraqi medical officials say the city's medical system was overwhelmed by a flood of civilian injuries, looting of hospital supplies and lawlessness on the streets that keeps medical personnel at home.
But Thursday, medical school students turned out to help at the Al-Kindi hospital, dressed in their blue smocks. Some combed the neighborhood for looted medical supplies and returned cheering to the hospital in a double decker bus.
The once-random and chaotic looting became systematized, with the German Embassy and the French Cultural Center, becoming the latest buildings to be plundered.
Some US forces received word Thursday that they should begin trying to stop the looting, but they were only just beginning to devise ways to do so.
"There's civilian looting like crazy, all over the place. There just aren't enough of us to clear it out," said US Marine Lance Cpl. Darren Pickard, who was trying to protect an Iraqi police academy from looters seeking the hundreds of rifles, grenades, knives, pistols and mortars from the academy's armory.
US Lt. Col. Michael Belcher, commander of the 3rd Battalion, 7th Marine Regiment, told officers Thursday to try to quell looting. "There's so much. How do you stop it?" Belcher said. "I'm a security force. I can fight, I can keep the peace. But police work is not our forte."
Civilians began bringing their wounded to the US military medics. Some Iraqis waved at soldiers and pointing at their stomachs, saying "Hungry! Hungry!" and begging for food. Other complained of a lack of water.
One hotel manager, who declined to give his name said: "There's one good thing only, Saddam has disappeared. Everything else is bad. There's no food. there's no water. and everyone is afraid." Meanwhile, smoke billowed from buildings across the city. US Marines said Iraqi holdouts were setting fire to their own quarters and blaming the Americans. In at least one case, however, looters were seen setting fire to some buildings in the Interior Ministry complex.
US troops occupied the Oil Ministry. But the nine-story Ministry of Transport building was gutted by fire, as was the Iraqi Olympic headquarters, while the Ministry of Education was partially burned.
Near the Interior Ministry, the office building of Saddam's son Odai stood damaged, its upper floors blackened.
A building on fire near the Interior Ministry was rocked for more than 15 minutes by deafening explosions apparently caused by ammunition and rockets stashed inside.
US Marines seized a palace on the northern outskirts of the capital early Thursday in a fierce, seven-hour battle, indicating that the fighting is far from over in Iraq. One Marine was killed and as many as 20 were wounded.
Marines also battled holdout fighters at a Baghdad mosque and the house of a leader of Saddam's Baath Party.
Around the city, looters hit stores and government installations, including the Irrigation Ministry, the Transport Ministry, the Air Force officers club, the government computer center, the Olympic hospital and state laboratories.
The German Embassy, a three-story off-white building in the center of al-Karada district, was also sacked. Looters emerged with air conditioners and computers and others cleaned out the French Cultural Center and Odai's house, the Arab- language TV network Al-Jazeera reported.
In the city center, donkey-drawn and horse-drawn carts were loaded with office furniture, TV sets, appliances and carpets. In Saddam City, a poor, densely populated Shiite Muslim section of Baghdad, residents set up roadblocks and confiscated loot, sending it to a mosque, said Imam Amar Al-Saadi.