The Associated Press

American and British forces advanced Friday through southern Iraq, some racing unimpeded across the desert, others meeting hostile fire. Hundreds of Iraqi soldiers surrendered and U.S. officials said Iraq's command structure appeared to have disintegrated.

The allies reported their first combat casualty, a U.S. Marine with the 1st Expeditionary Force killed in southern Iraq. According to a comrade, the Marine was shot in the stomach while his company was sweeping around a burning oil pumping station.

Twelve more Marines -- eight British and four American -- died when their helicopter crashed and burned in Kuwait. Officials said the crash was not caused by hostile fire.

Waving Iraqi civilians greeted members of the 1st Marine Division as they entered the town of Safwan. Using winch chains, some of the troops hauled down giant portraits of Saddam overlooking a street.

"We're very happy… Saddam Hussein is a butcher," said a man in the back of a pickup truck, identifying himself only as Abdullah. A woman fell at the feet of the Americans and embraced them, touching their knees.

In western Iraq, U.S. forces seized two airfields, a pivotal first step toward opening up another front in the war.

Hoping the regime might capitulate, U.S. military commanders held back-channel negotiations with Iraqi commanders and refrained from all-out bombardment. Instead, U.S. missiles and bombs struck specific targets -- including the main presidential palace in Baghdad and strongholds of the elite Special Republican Guard.

Iraqi Information Minister Mohammed Sa'eed al-Sahhaf said one of Saddam Hussein's homes was hit in the bombing, though no one was hurt.

U.S. officials said they had no definitive word on whether the Iraqi leader was caught in the attack, but indicated that medical workers were summoned to a compound in Baghdad after it was hit. The officials said Iraqi forces subsequently seemed cut off from their leadership.

The official Iraqi News Agency said 37 people were injured in the latest strikes on Baghdad, and Iraqi military said four soldiers were killed. There were no figures given on Iraqi losses in ground combat.

Thousands of American anti-war activists protested, blocking streets, boycotting classes and chaining themselves together. More than 1,500 people were arrested, mostly at a raucous demonstration in San Francisco.

U.S. and British forces moved on a broad front, with infantry racing across the desert in thousands of tanks and trucks, plumes of dust in their wake, and Marines edging cautiously toward strategic oil towns and military outposts, calling in air support to take out snipers. In some cases, units were preceded by special forces teams.

"There are signs of continuing Iraqi desertions and disagreement and division in all levels of the regime," said British Prime Minister Tony Blair.