Baghdad, Iraq ? Attackers fired a rocket-propelled grenade at an ambulance carrying a wounded U.S. soldier Thursday south of Baghdad, killing one American and injuring two others — the latest in a rapid-fire series of assaults on U.S. occupation forces.

The violence came as hundreds of people marched in a funeral procession for a former Iraqi army officer killed by U.S. troops, shouting “Death to Bush!” and “Revenge!”

Attackers also fired a rocket-propelled grenade at a U.S. tank north of Baghdad, and a U.S. Army truck was set afire in the western part of the capital. The military reported that three mortar shells hit outside a coalition-run aid office Tuesday in the town of Samarra, killing one Iraqi and wounding 12.

U.S. forces in Iraq are being hit with guerrilla-style attacks despite an intense crackdown that this week has seen the arrests of hundreds of people across Iraq.

In Washington, Secretary of Defense Donald Rumsfeld said Wednesday that the resistance was coming from “small elements” of 10 or 20 people without any central control. Baghdad has less violent crime than the U.S. capital, he said.

Yet the increasingly common sight of U.S. vehicles burning on the streets of Baghdad and American soldiers evacuating their dead and wounded speaks to grave dangers facing U.S. forces trying to police and rebuild postwar Iraq.

Saddam Hussein loyalists, radical Sunni Muslims, non-Iraqi “holy warriors” and disgruntled ex-army soldiers are all said to be staging attacks.

“There are reports that leaflets, calling Iraqis to armed resistance against the coalition and offering rewards for killing coalition members, are being distributed,” the United Nations mission in Iraq said in a statement Thursday.

The uneasy coexistence between Iraqis and their American occupiers was evident at the house of Tareq Hussein Mohammed, a 32-year-old army officer shot dead Wednesday by U.S. troops during a protest by former Iraqi army personnel demanding their wages.

As his body was carried into the house, dozens of mourners fired Kalashnikov assault rifles into the air and cursed the United States — a show of respect for the dead and defiance of U.S. authorities who have banned firing weapons in the street.

Mohammed was one of two men shot outside the gate of the Republican Palace, a presidential compound now serving as the U.S.-led coalition’s headquarters in Baghdad. The U.S. military said the men were shot when the protest turned violent.

“Abu Soheib, come back to us,” wailed his wife, Soheir, using his nickname. “Now there is no salary, and no man.”

“America is taking oil and we are taking bullets,” said another relative, Salawa Mohammed.