The US army says it may send more troops to Iraq before the January elections, depending on the outcome of its offensive in Falluja.
The assault on Falluja is aimed at stabilising the country
US military commanders were considering whether to boost their troop levels in Iraq by several thousand, Lt Gen Lance Smith told a Pentagon news conference.
Gen Smith, the deputy head of US Central Command in Iraq, described the Falluja operation as very successful.
But insurgents continue to hold out in some parts of the city.
And Gen Smith said it was "too early to say" if it had broken rebels' resistance.
His remarks contrasted with those of the top marine commander in Iraq, Lt Gen John Sattler, who said on Thursday that the offensive had indeed "broken the back of the insurgency".
In further violence on Saturday, Iraqi insurgents used rocket-propelled grenades to attack a police station in Baghdad's north-western area of Adhamiya.
One report said three policemen had been killed in the fighting, which lasted for about five hours.
The police station has been attacked many times before, but the timing of this latest assault may be significant, says the BBC's Richard Galpin in Baghdad.
On Friday, Iraqi national guards, with support from American troops, raided the Abu Hanifa mosque in the same district and tried to search for militants who had fled from Falluja.
Two worshippers were killed in the attack on one of the most important Sunni mosques in Iraq.
In other developments:
- US troops reported to be blocking roads into the western city of Ramadi and urging residents to stay indoors
- Four decapitated bodies are found by US troops in the northern city of Mosul
- Influential Qatar-based cleric Sheikh Youssef al-Qaradawi says Muslims have a duty to resist the American and other foreign military forces in the country.
The US-led assault on the Sunni Muslim city of Falluja, 50km (30 miles) west of the capital, Baghdad, is aimed at stabilising the country before the elections.
Gen Smith said polling was likely to take place on 27 January and the signs were that Iraqis were looking forward to voting, despite the threat of violence.
However, he said the "widespread campaign of intimidation" by insurgents would be hard to bring under control before the vote took place.
Gen Smith said US commanders could boost troop strength in Iraq ahead of the elections by about a brigade - in other words, by 3,000 to 5,000.
There are about 138,000 US troops in the country. Initially, the plan would be to ask troops currently there to stay on longer than originally intended.
The Pentagon has already announced one temporary increase of about 3,000 troops.
US forces in Falluja continue to fight what commanders say are the last pockets of insurgent fighters hiding in the south of the city.
Artillery, tank shells and bombs fell on the area for much of the night and the boom of artillery fire continued into Saturday morning.
The marine commander says these are the final bands of fighters in Falluja but they are proving difficult to dislodge.
The US military officers say they hope to have the fighters cleared out by the end of the weekend.
Many homes in the Martyrs' neighbourhood have been reduced to rubble.
This tactic may be part of the insurgents plan to sway public opinion against the American forces, says the BBC's Jennifer Glasse who is embedded with US marines there.