Twenty militiamen were killed when US tanks smashed through the gates of a mosque and opened fire on Sunday.
Bloodstains, spent cartridges and the imprints of tank tracks marked the site of the fighting, which comes as occupation forces launch more violent attacks on Shia cleric Muqtada al-Sadr's Mahdi Army.
Another 12 died in various attacks on occupation forces, according the the US army's 1st Armored Division.
The US military said those killed were all members of the Mahdi Army, which has been involved in a month of bitter fighting with US troops in nearby Najaf and in Karbala.
US soldiers killed
Soldiers at the scene of the Iraqi resistance ambush on US troops near Falluja said a vehicle apparently loaded with explosives blew up on Sunday as a convoy of US marines and army personnel passed by.
They said that assailants then opened fire with rocket-propelled grenades from a grove of palm trees.
The attack was the first major loss inflicted on US troops in the area since the end of an offensive they launched last month in Falluja - a hotbed of resistance activity - after four US contractors were killed and their bodies mutilated in the city.
Falluja was the scene of heavy
fighting until a deal on 10 May
US marines withdrew from the city earlier this month and handed over control of security in Falluja to a force including
officers from ousted Iraqi strongman Saddam Hussein's army.
Toll breaks 800
The deaths brought US losses in Iraq to 801 since the start of the US-led invasion in March 2003.
It was the first time since the marines ended a month-long offensive in Falluja in early May that they had confirmed a death in action near the town.
There have been other deaths in al-Anbar province, west of the capital, of which Falluja forms part, but US military spokesmen have declined to specify where they took place.
Occupation forces has been braced for an upsurge in resistance ahead of its 30 June deadline for the handover of partial sovereignty to a provisional government.
List of names
Meanwhile, a US marine officer provided Iraqi authorities with the names of 25 people sought in the killing of the four American civilian contractors.
"This is a priority for the coalition troops that they take action against those people implicated in the murders," Col John Toolan, commander of the 1st Marine Regiment, told reporters after handing the list to Falluja's police chief, Sabr Fadil al-Janabi.
The US is hunting down the killers
of the four US contractors
Names of the 25 people were not released, but Toolan described them as a mix of Falluja residents and outsiders. He would not say whether any of them were non-Iraqi "foreign fighters".
"You are responsible for investigation, if you were to identify and apprehend those people responsible, it would go a long way in building trust with the coalition forces," Toolan told al-Janabi.
Toolan said the suspects would be tried in an Iraqi court before an Iraqi judge.
He expressed confidence that the police chief would follow up on the request but acknowledged it would be difficult in a city where anti-US feeling is as high as anywhere in Iraq.
"We'll see how it turns out," Toolan said. "It's going to be a tough job to make the arrests."