The tough fight put up by insurgents in Falluja, west of Baghdad, prompted the marine commander to make comparisons with the Vietnam War.
As the day drew to a close, sniper fire and mortars were being fired around the main marine compound in the industrial area on the eastern edge of town, where rocket fire and mortars fell short all day.
"Marines southwest of Falluja were attacked by an unknown number of enemy forces in buildings using machine guns, small arms, hand grenades and RPGs (rocket-propelled grenades)," said a military statement.
"The marines called in reinforcements and attacked the enemy positions, destroying a truck with a mounted machine gun and the building that the attackers were firing from. Ten enemy combatants were confirmed killed."
The statement also said about 30 insurgents had been killed in the Al-Anbar province, home to Fallujah, but mostly in clashes in other marine operations in nearby Ramadi. Neither claim could be verified.
Later in the day the US military said it had suffered six more combat deaths in Iraq, bringing to 449 the number of soldiers killed in combat since the invasion.
Forty US troops have been killed across Iraq in the past week
In a statement, it said five soldiers had been killed in action on Wednesday and Thursday, and added that another soldier had died after being wounded in a bomb attack on 4 April in the northern city of Mosul.
Forty US troops have been killed across Iraq in the past week.
Throughout the day US occupation forces inched forward block-by-block taking sniper fire and hit-and-run attacks with mortars and RPGs. A US medic said the resistance was more intense than in last spring's invasion.
Mortars and small-arms fire were launched by small groups of insurgents who appeared in alleyways or on rooftops, only to melt away.
The thud of mortar rounds echoed around the town and plumes of smoke dotted the landscape. Machine-gun fire rattled through the streets as F-16 warplanes buzzed overhead.
After more than three days of ferocious fighting, the marines had managed to move just two kilometres (a little over a mile) through the industrial zone, which they had thought was largely abandoned.
They stopped their advance in the afternoon to wait for reinforcements from another battalion.
US marines give first aid to a
wounded comrade near Falluja
The flames of exploding rockets lit the sky as the marines came under repeated mortar and RPG fire from factories, homes and mosques.
"MOUT (Military Operations in Urban Terrain) is the most intense kind of fighting," said Lieutenant Colonel Brennan Byrne, a battalion commander.
"And this is like Hue City in Vietnam," he said, referring to the former imperial capital where in 1968 US troops faced the most ferocious street fighting of the communists' decisive Tet offensive.
Marines, who took part in defeating Saddam's armed forces a year ago, said the resistance they were now facing was tougher than anything thrown at them by the old regime's once vaunted Republican Guards.
Sergeant James Ramsel, of the battalion's Alpha Company, said there had been no let-up in the resistance. "It's been going on all night; it's still going on."
Hospital sources cited by Al-Jazeera said a total of 105 Iraqis had been killed in Falluja since Tuesday evening.
The ferocity of the fighting stopped some corpses from being cleared from the streets.
Flies buzzed over the body of a middle-aged man with a mustache, shot in the neck by marines after he fired a RPG at them across the industrial wasteland of garages, factories and metal shops.
US forces pinned down
Captain Chris Chown, a marine battalion air officer, conceded that the insurgents were proving not only determined but also adept at using guerrilla attacks to counter the US advantage in equipment and numbers.
Fighters celebrate in front of a
burning US convoy near Falluja
"One guy can basically hold down a whole squad. He shoots from one window and pops in another. They are fierce and very determined but they can't shoot straight. They are basically spraying and praying."
However, Chown expressed concern the outgunned Iraqis could still end up winning the battle of public opinion if the fighting continued.
"I hope one day we don't get so jaded we just roll down the streets in armoured vehicles shooting at whatever moves," she said.
"If that happens we need to take a step back and look at the humanity of the place or we've just lost our mission."
"We are at a crossroads in Falluja... You get to a critical juncture where one small event is going to tip things for us or against us."