The US is examining the possibility of sending more troops to Iraq if the situation there gets out of control, a top Central Command official has said.
Sadr loyalists celebrate in Baghdad after clashes with coalition troops
The official confirmed that commanders had been asked to present such options, but said the US military did not believe it was needed.
The comments came on the second day of anti-coalition protests by supporters of radical Shia cleric Moqtada Sadr.
The US-led coalition said it had issued an arrest warrant for Mr Sadr.
A coalition spokesman said earlier that the warrant was in connection with the murder of a rival cleric a year ago.
Mr Sadr has denied any involvement in the killing of Abdel-Majid al-Khoei in Najaf in April 2003.
He has barricaded himself with armed supporters in a mosque in Kufa, south of Baghdad.
On Monday, US helicopter gunships targeted militia members loyal to Mr Sadr in the mainly Shia district of al-Shuala in Baghdad.
The BBC's Justin Webb says President George W Bush is coming under increasing pressure over his Iraq policy.
Prominent Democratic Senator Edward Kennedy has called the war Mr Bush's Vietnam.
His remarks were dismissed by Republicans, but the most recent opinion poll seems to suggest that on the subject of Iraq, public opinion is shifting rapidly away from the White House.
Planning 'worse-case scenarios'
"The events of the weekend show an obvious potential for more demonstrations and more violence," a Central Command official told reporters at the Pentagon on condition of anonymity.
"We asked our staff to look at what forces might be available in quick-response mode."
But the official said the request had been made "as a matter of planning", and the US military had "adequate forces" in Iraq.
There are currently about 134,000 US troops in Iraq, the official said. They are part of the 155,000-strong coalition force.
"We always plan worse-case scenarios. And clearly if this thing got out of control over there we would have to start looking at the number of forces that we have," the official said.
And referring to the Shia protests across Iraq, he said "we can't even begin to call that a Shia uprising".
The protests were triggered by the closure of Mr Sadr's al-Hawza newspaper a week ago on the grounds that it was inciting violence.
They intensified after the arrest on Saturday of one of Mr Sadr's top aides, Mustafa Yacoubi, in connection with Mr Khoei's murder.
The coalition accuses Mr Sadr of trying to usurp its power and says the revolt will not be tolerated.
Many of Iraq's majority Shia Muslims, repressed under Saddam Hussein, welcomed last year's US-led invasion, and attacks on coalition forces were largely confined to the minority Sunni community before Sunday's violence.
However, Mr Sadr has become an increasingly outspoken opponent of the occupation.
The US administrator in Iraq, Paul Bremer, said on Monday that Mr Sadr's followers had effectively placed themselves outside the law.
But Mr Sadr responded by saying he was "proud" to be considered an outlaw by the US.
At least 13 coalition soldiers and 46 Iraqis have died in confrontations related to the protests.
The latest US casualties were four Marines killed in action in the western Anbar province, the military said on Tuesday.
There has been continuing tension in Sadr City, a district which saw eight US troops and a reported 22 Iraqis killed in fighting on Sunday.
US troops also began an offensive in Falluja, a Sunni town where four Americans were killed and mutilated last week.