Samarra, Iraq ? One of the bloodiest engagements since the fall of Saddam Hussein showed a new, deadlier side of the Iraqi insurgency: stepped up, coordinated assaults by groups of guerrillas bent on battle rather than a hit-and-run attack, the U.S. military said Monday.

“Here it seems they had the training to stand and fight,” said Capt. Andy Deponai, whose tank was hit by a rocket-propelled grenade during the firefight Sunday in Samarra, north of Baghdad.

Residents disputed U.S. assertions that dozens of Iraqi fighters died, saying fewer than 10 were killed and that most of those were civilians.

The well-coordinated ambushes signaled an escalation of guerrilla tactics, although the attack in Samarra was unsuccessful. A dozen cars lay gutted and wrecked Monday in the streets, and bullet holes pocked many buildings. A mosque and a kindergarten also were damaged.

Brig. Gen. Mark Kimmitt said that in one of the ambushes, a dozen attackers dashed out of a mosque and opened fire on U.S. military vehicles. They also fired from alleyways and rooftops.

“It was a large group of people,” Kimmitt said in Baghdad. “Are we looking at this one closely? Yes. Is this something larger than we’ve seen over the past couple of months? Yes. Are we concerned about it? We’ll look at it and take appropriate measures in future operations.”

Insurgents struck elsewhere Monday. West of Baghdad, gunmen ambushed a U.S. military convoy, killing one soldier, the U.S. military said. The attack with small-arms fire occurred near Habbaniyah, 50 miles west of Baghdad, the military said.

A U.S. Army general said Iraqi insurgents in Baghdad appeared to have a central leadership that financed attacks and instructed eight to 12 rebel bands operating in the city when to attack and when to lie low.

But Brig. Gen. Martin Dempsey said the instructions were not specific.

“The manner of attack is up to the individual bands as long as the efforts disrupt and discredit the U.S.-led coalition and any progress it has made,” said Dempsey, who commands the Army’s 1st Armored Division, which controls Baghdad and the surrounding region.

Iraqis inspect cars destroyed during Sunday's gun battle in Samarra, Iraq, some 60 miles north of Baghdad. U.S. forces used tanks and cannons to fight their way out of simultaneous ambushes by Iraqi insurgents.

He said he thought a recent lull in attacks in Baghdad stemmed from an order to refrain from action during coalition offensives against guerrilla targets.

The fighting in Samarra, 60 miles north of the Iraqi capital, represented a greater level of coordination in the Iraqi insurgency, although U.S. forces said they had anticipated the attacks and blunted them with superior firepower.

“It’s hard to tell on the basis of one attack exactly what tactics may or may not be changing,” Gen. Peter Pace, vice chairman of the U.S. Joint Chiefs of Staff, said at a news conference with Defense Secretary Donald H. Rumsfeld in Brussels.

“The fact is that in this particular case, about 50 or so of the enemy did collect together for whatever reason they thought was appropriate,” Pace said. “They attacked and they were killed. So I think it’ll be instructive to them for future analysis when they’re thinking about what they’re going to do next.”

The U.S. military said 54 Iraqis were killed. But Iraqi residents and hospital officials said the toll was much lower.

Five American soldiers were wounded, the U.S. military said. Soldiers said there was sustained firing at both banks for about 45 minutes, but that heavy fire from U.S. tanks and Bradley fighting vehicles overwhelmed the attackers.

U.S. commanders said some of the insurgents were wearing dark clothing and scarves over their faces, the favored garb of Saddam’s Fedayeen paramilitary force.