The top commander in Iraq, U.S. Army Lt. Gen. Ricardo Sanchez, said a Shiite militia has at least partial control over two southern cities, Kut and Najaf. He said coalition forces will move soon to break the militia's hold in an operation dubbed "Resolute Sword."
There were also signs that Shiite militia controlled Kufa.
Fighting this week has left 36 Americans and at least 459 Iraqis dead. This includes more than 280 Iraqis killed since the Marines' siege against insurgents in Fallujah, west of Baghdad, began early Monday said Taher Al-Issawi, the director of the city's hospital.
The intensified violence on two fronts — one Sunni, one Shiite — has forced the U.S. military to consider sending more troops to Iraq and to postpone the removal of forces due to rotate out.
"You can be certain that if they want more troops, we will sign deployment orders so that they'll have the troops they need," Defense Secretary Donald H. Rumsfeld said at a Pentagon news conference Wednesday, though he insisted fighting was not spinning out of control.
Sanchez said it appeared there are links "at the lowest levels" between the Shiite and Sunni fighters.
In other developments:
The United States has about 135,000 troops in Iraq. The continuing rotation of forces in Iraq gives American forces an advantage by having about 20,000 more troops than would otherwise be there.
Gen. John Abizaid, the U.S. commander of the Iraq campaign, spoke with President Bush Wednesday and did not ask for more troops then, a senior defense official said on condition of anonymity.
Some members of Congress said they believed more American troops should be sent to Iraq.
Democratic Sen. Robert Byrd, the Senate's senior member and a fierce critic of the war, said he heard "echoes of Vietnam" in the talk of increasing U.S. forces in Iraq.
In response, Sen. Gordon Smith, a Republican, paraphrased Ho Chi Minh, noting that the North Vietnamese leader said the Vietnam War was won by dividing the American public, not on the battlefield.
"We must win," Smith said. "We must not have the will of the American people broken by the naysayers."
Gen. Richard Myers, chairman of the Joint Chiefs of Staff, said fighting in Iraq came in two broad categories.
West of Baghdad in cities such as Fallujah and Ramadi — where 12 Marines were killed Tuesday — the main opposition is "former regime loyalists," including supporters of former president Saddam Hussein and anti-American foreign fighters loyal to Abu Musab al-Zarqawi, a Jordanian-born terrorist believed linked to al Qaeda, he said.
The fighting in the south — which on Wednesday spread for the first time to central Iraq — is waged by the Shiite Al-Mahdi Army militia, which launched a wave of attacks against coalition troops in southern cities and Baghdad this week after U.S. authorities began a crackdown on its leader, al-Sadr.
Rumsfeld discounted the strength of al-Sadr's militia. "There's nothing like an army," he said. "You have a small number of terrorists and militias coupled with some protests." U.S. officials estimate al-Sadr's force at about 3,000 fighters.
But The New York Times reports intelligence officials believe that the uprising goes well beyond al-Sadr's force. And the week's fighting showed a strength that few expected from the al-Mahdi Army.
That militia virtually controlled the Shiite southern cities of Kut and Kufa and were in partial control of Najaf.
Al-Sadr fighters battled American troops in the town of Baqouba, northeast of Baghdad — the farthest north that the Shiite violence has reached.
Overnight, al-Sadr militiamen battled with Polish troops in the city of Karbala throughout the night and with Spaniards in Diwaniya and Najaf. Nine Iraqis were killed in Karbala, the Poles said.
Police in the cities have abandoned their stations or stood aside as the gunmen roam the streets. Their performance raises questions over a force U.S. leaders are counting on to keep security in the future Iraq.
In Baghdad, U.S. forces before dawn struck and damaged al-Sadr's office in his main stronghold, the sprawling Shiite neighborhood of Sadr City, residents said.
In Fallujah, Marines battled again around the Abdel-Aziz al-Samarrai mosque, which Marine Capt. James Edge said insurgents were again using as a base despite a six-hour battle the day before to uproot them. Helicopters were deployed to support the Marines, he said.
Iraqi witnesses said some 40 people gathering for prayers were killed in a U.S. airstrike on the mosque compound, but U.S. officials said they had no report of civilians killed.
Brig. Gen. Mark Kimmitt said U.S. Marines did not attack the mosque until it became clear enemy fighters were inside and using it to cover their attacks.
Heavy fighting was heard Thursday in several neighborhoods, and U.S. Marines grabbed rooftops of buildings, firing on gunmen in the streets.