Two US marines have been shot dead in the Iraqi city of Falluja.
Marines are clearing houses after the US-led offensive in Falluja
Lt Gen John Sattler said a group of marines was ambushed during house-clearing operations and returned fire, killing three insurgents.
Meanwhile, Iraqi troops in Falluja are reported to have found a laboratory with explosives materials and instructions for making anthrax.
Iraq's interim security minister said 2,000 people had been killed in the US-led offensive in the city.
Kassim Daoud also said 1,600 people had been detained in the operation.
Mr Daoud said a man described as a key aide to the Islamic militant Abu Musab al-Zarqawi had been arrested in the northern city of Mosul. He gave few other details.
A US army intelligence officer has said the assault on Falluja has not turned up any new leads on the whereabouts of the fugitive Zarqawi, who is alleged to have used the city as his base.
Maj Jim West told the Reuters news agency the objective of the assault was "not Zarqawi, it was defeating the insurgents for the people of Falluja".
A rebel organisation claiming to be from the city has told an Islamist website it has regrouped to mount new attacks on US forces and their Iraqi allies.
Clashes in the shattered city intensified on Friday, the French news agency AFP reports.
In other developments:
- Four employees of a British security firm are killed in a rocket attack on Baghdad's heavily-fortified Green Zone
- Iraqi and US forces appear to have regained control over the town of Latifiya, a hotspot in the so-called "Triangle of Death", south of Baghdad
- US forces discover 13 bodies in the northern city of Mosul, bringing to 35 the total number found there in the last week
Iraqi interim Security Minister Kassim Daoud said Iraqi soldiers had discovered a suspected weapons-making factory in the south-west of Falluja.
"They also found in the lab booklets and instructions on how to make bombs and poisons. They even talked about the production of anthrax," he told a news conference.
But there was no indication the lab had been used to manufacture chemical weapons, a US marine spokesman said.
However, the marines said an arsenal of conventional weapons they uncovered in a mosque in eastern Falluja was large enough to support a nationwide rebellion.
The "stunning" finds included mortars, bomb-making equipment, grenades and rockets, officials said.
Lt Gen Sattler said US-led troops had now cleared about half the houses in the city.
"We will continue to clear out houses till every one is secure, We've taken more and more of their safe houses. They're running out of places to hide," he said.
US marines have said it may be several weeks before civilians who fled the city can return.
Lt Gen Sattler vowed that the city would be safe in time for January's elections. "We want every Fallujan to vote from their house," he said.
More than 50 US marines died and more than 400 were wounded in the assault.