BAGHDAD, Iraq -- Nineteen Iraqi army soldiers were killed and four wounded yesterday when insurgents exploded a roadside bomb to cripple an army convoy northeast of Baghdad and then opened fire on the patrol, police said.

The carefully coordinated attack near the town of Adhaim triggered a 30-minute firefight that killed two other people, possibly insurgents, and left five civilians wounded.

It was the second major strike in three days against U.S. and Iraqi forces that defend the Shiite Muslim-led government against a predominately Sunni Arab guerrilla uprising. A powerful bomb fashioned from several artillery shells Thursday killed 10 Marines near Fallujah in the deadliest attack against U.S. forces in nearly four months.

The Islamic Army of Iraq, a militant group believed to be linked to deposed President Saddam Hussein's Baath Party, posted a video yesterday showing what it called an explosion against a U.S. patrol in the Fallujah area. It did not directly link the footage to Thursday's attack, which police said occurred on a road west of the city, which is about 30 miles west of Baghdad, the capital.

In the brief video, a Humvee flanked by what look like U.S. troops on foot travels slowly along a street. An explosion engulfs the vehicle, sending clouds of dust into the air and bystanders fleeing.

The video's authenticity could not be verified. It was shown on Al Jazeera television and later posted on a Web site used by insurgent groups to claim attacks.

Yesterday's ambush targeted the Iraqi army, which the U.S. military is expanding and training to take on the insurgents. President Bush last week acknowledged the Iraqi army's "uneven" performance but said its troops eventually would be ready to shoulder the burden of maintaining the nation's security.

During the morning attack yesterday, all five of the Iraqi convoy's vehicles went up in flames.

The soldiers leapt out into the road where "there was very heavy shooting at us from all directions, and nowhere to hide," said Ismail Fatah, a soldier in the Salam Battalion.

"We shot back indiscriminately," he added. "We may have caused some casualties among the civilians standing nearby."

The insurgents faded away as army and police reinforcements arrived from nearby Baqubah, the capital of Diyala Province, about 35 miles northeast of Baghdad.

Baqubah, a tense city with a mixed population of Shiites and Sunnis, lies on a fault line of the sectarian conflict. It has experienced a surge in guerrilla activity over the past three weeks, prompting the army to bring in fresh troops. The battalion attacked yesterday was made up of soldiers from Shiite cities in southern Iraq.

The attack was one of the deadliest on Iraqi soldiers since a June 15 suicide bombing at a mess hall north of Baghdad that resulted in the deaths of at least 23 soldiers.

Earlier in the day, rocket or mortar fire struck a U.S. base at the airport in Mosul, wounding two American soldiers, the U.S. military said. The city is about 225 miles northwest of Baghdad.