Baghdad, Iraq ? Even as American officials expressed cautious optimism about the first 24 hours of a militia cease-fire in southern Iraq and continued to hope that a recently appointed Iraqi government would bring peace to the nation, yet another day of grisly violence broke out Saturday in Baghdad.

In the first attack, a roadside bomb killed two U.S. soldiers and injured two others in the early-morning hours near the restive Baghdad neighborhood of Sadr City. It was the same section of town in which four soldiers had been killed and five wounded the previous day.

Later in the afternoon, a convoy was ambushed near the Baghdad airport. Although U.S. officials did not provide either a body count or a description of the events, witnesses at the scene said at least four people died. The identities of the dead were not known, but the sport utility vehicles engulfed in fire and smoke after the attack were the sort used by civilian contractors in Iraq.

Safar Khamis, an Iraqi police recruiter who said he saw the ambush, said that a car of Iraqis opened fire at the convoy with rocket propelled grenades from one side of the road as another group of men began shooting AK-47s from the other direction.

One of the burned-out SUVs was a white Toyota Land Cruiser filled with Iraqi civilians who happened to be passing by at the wrong time, Khamis said. The second SUV, a white GMC, was carrying westerners and accompanied by military Humvees, he said.

After the Land Cruiser was hit, the driver, his face covered in blood, leaned out the window and yelled that there were women and children inside the vehicle, and they were burning to death, Khamis said. Onlookers were unable to respond because of the crossfire.

Mustafa Mohammed, 14, said he could hear people screaming and glass breaking as the SUVs went up in flames.

To the west of Baghdad a civilian contractor was killed and a soldier wounded in a roadside bomb attack on their convoy near the town of Haditha, according to the U.S. military.

In the southern cities of Najaf and Kufa, sites of recent intense battles between the U.S. Army and fighters loyal to Muslim cleric Moqtada al-Sadr, militia members reportedly began putting down their arms.

Iraqi militants loyal to Shiite cleric Muqtada al-Sadr fire a mortar at U.S. troops Saturday in the Baghdad district of Sadr City. Two U.S. soldiers were killed early Saturday by a roadside bomb near Sadr City.

Film footage showed shops open on the streets of Najaf, which just the day before had been filled with swarms of gunmen. An arrest warrant is still outstanding for al-Sadr, accused of being involved in the murder of a rival cleric.