Fighting between US forces and Sunni Iraqi militants in the city of Falluja has killed at least 36 Iraqis.
Falluja has been a centre of anti-US resistance
Helicopter gunships have been bombarding targets in the city which is ringed by heavily armed marines tasked with "pacifying" the flashpoint.
Reports say that Falluja mosques are broadcasting a call for "Holy War" and armed women are among the militants.
US forces took action after four Americans were killed and their bodies dragged through the streets last week.
Population: 284,500 (2004 estimate, World Gazetteer)
Predominantly Sunni Muslim with an estimated 70 mosques
Benefited from heavy investment in factories under Saddam
Hospital sources in Falluja said many more Iraqis were wounded in overnight fighting as marines moved into an industrial zone on the outskirts.
A correspondent for Qatari broadcaster al-Jazeera TV reported from inside the town on Wednesday that food supplies were running low and smoke was pouring from burning houses in the area of the marines' advance.
Reporting "fierce battles" in the east and north-west, he added that gunmen were fighting back with rockets.
Fighting has also erupted in other "Sunni Triangle" towns, with 12 US marines killed at Ramadi on Tuesday, while an unprecedented revolt by Shia Muslim militants continues to rage elsewhere in Iraq.
Call to war
The Associated Press news agency quotes witnesses in Falluja as saying that the mosques have been calling for a "jihad" as gunmen and marines fight running battles in the east of the town and in the centre.
Armed women were in the streets and some gunmen could be seen carrying mortars.
Abd-al-Wahab al-Qaysi, described as a local "notable", told al-Jazeera that local people were determined to resist.
"We have to hold out, fight and struggle," he said, speaking at a cemetery where victims of the fighting were being buried.
"This is our land. We did not attack America. It is America that attacked us. It travelled thousands of kilometres across the oceans to attack us."
The marine assault on Falluja comes after four US civilian contractors were ambushed there and their bodies mutilated and strung from a bridge by a mob on 31 March.
US commanders vowed to track down the killers and troops now in Falluja are carrying photographs of "a good many" suspects, US Defence Secretary Donald Rumsfeld said on Tuesday.
"It will be a methodical effort to find the individuals who were involved," he added.