Bombs and artillery have thundered across Baghdad as US forces tighten their grip on the capital's outskirts, bringing up more troops and cutting approaches on three sides of the embattled city.
The 18th day of the war to topple Iraqi President Saddam Hussein also saw fierce offensives in Basra, where British tanks pierced the heart of Iraq's second city, and Kerbala where US troops fought Iraqi paramilitaries street by street.
In northern Iraq on Sunday, Kurdish fighters said they had captured the town of Ain Sifni, northeast of Mosul, which is the third largest city in Iraq.
Thousands of Baghdad residents fled to escape the battle for Saddam's capital, the war's greatest prize. The Iraqi government banned travel in or out of the city between 6 p.m. and 6 a.m.
US artillery and planes kept up a relentless bombardment as armoured columns circled the fringes of the sprawling city of five million people.
For the first time in the war, mortar bombs landed in the centre of the Iraqi capital, hitting a commercial and residential area.
"US military estimates Iraqi military casualties at around 2,000 since we started attacking the outskirts of Baghdad," Major Rumy Neilson-Green said at US war headquarters in Qatar.
Signs of heavy bombardment were evident in demolished houses and holes in the concrete walls of government buildings and houses along the Mahmoudiya highway in the south of the city, Reuters correspondent Hassan Hafidh said.
Iraqi Information Minister Mohammed Saeed al-Sahaf said forces loyal to Saddam continued to fight invading troops.
"The valiant Republican Guards are encircling the enemy near the airport. We destroyed six tanks and damaged 10 others and killed 50 of the enemies' forces," Sahaf told a news conference.
"After crushing the American and British aggression and invasion there will only be Iraq, headed by Saddam Hussein with all its traditions...and all its institutions," he said.
Iraqis chanting "Long live Saddam Hussein" crowded around a destroyed US tank on a highway leading south out of Baghdad where Iraqi officers said four US soldiers were killed.
Reuters correspondent Sean Maguire, with US troops 22 miles south of the city, saw a burned out M1-A1 tank. US officials told him American forces lost two of the tanks, considered the most formidable in the world, on Friday.
US-led forces dropped 200,000 leaflets over Baghdad, urging civilians to stay inside for their safety, a spokesman said at war headquarters in Qatar.
Figures for the number of civilians killed or injured in Baghdad were not available but International Committee of the Red Cross spokesman Roland Huguenin-Benjamin in Baghdad told Reuters on Sunday, "During fierce bombardment, hospitals received up to 100 casualties per hour."
With many medical staff unable to reach the hospital due to the bombing, doctors were performing everything from surgery to taking blood, giving injections and ferrying the wounded.
"I've been a doctor for 25 years and this is the worst I've seen in terms of number of casualties and fatal wounds," said Dr. Osama Saleh al-Duleimi, 48, who witnessed the 1980-88 Iran-Iraq war and the 1991 Gulf War.
An ICRC spokeswoman in Geneva said the situation in the city was becoming desperate.
"The situation is extremely problematic now in terms of clean water supply and sewage evacuation. Everybody now is operating on backup generators as there is hardly any power any more," said Antonella Notari.
US military officials said American and British troops were tightening their noose on the Iraqi capital.
Colonel John Peabody, commander of the Engineer Brigade of the 3rd Infantry Division, told Reuters correspondent Luke Baker there were now about 7,000 troops at the airport southwest of the capital - roughly a fourfold increase on initial levels.
US military sources also said troops have seized control of two major highways leading out of Baghdad.
A force of about 50 tanks and 70 Bradley fighting vehicles took control of Highway 1 leading north out of Baghdad and Highway 10 leading west, US military sources said.
"You can see we've now seized control of the northwest shoulder of the city," one source said.
Marine units were also reported east of Baghdad.