Fallujah, Iraq ? Insurgents killed one U.S. soldier and wounded three others Sunday outside the troubled city of Fallujah, a day after angry protesters fired weapons and called for violence against the American occupation to protest one of the most serious friendly fire incidents of the Iraq war.

Early today, dozens of U.S. troops raided homes in Tikrit, Saddam Hussein’s hometown, and arrested five men suspected of helping to bankroll attacks against American troops.

“These individuals are involved in financing Fedayeen activity and organizing cells of resistance against U.S. forces,” said Maj. Bryan Luke of the Army’s 4th Infantry Division. No shots were fired in the early morning raid.

The U.S. administrator for Iraq on Sunday commented publicly on the accidental killing of eight Iraqi policemen by U.S. forces who mistook them for guerillas. He called the incident regrettable and suggesting victims’ families might be compensated.

“The very regrettable incident in Fallujah is still under investigation by our military. We have expressed regrets for it publicly,” Paul Bremer said at a news conference with visiting Secretary of State Colin Powell.

Powell arrived Sunday in Baghdad for his first visit since the U.S.-led ouster of Saddam Hussein. He said he was encouraged by progress toward self-rule.

He stood fast against growing international pressure to quickly turn responsibility for running the country back to Iraqis.

“The worst thing that could happen is for us to push this process too quickly before the capacity for governance is there and the basis for legitimacy is there and see it fail,” Powell said.

The death of the U.S. soldier outside Fallujah brought to 155 the number of American troops killed in Iraq since President Bush declared an end to major combat on May 1. During the heavy fighting before that date, 138 soldiers died.

An American soldier from the 1st Battalion, 22nd infantry regiment, 4th Infantry division in Tikrit, Iraq, keeps watch over the fence at a suspected Saddam loyalist house during a raid. Five men were taken into custody early today, and a large cache of weapons and money were found during the raid.

The military provided few details, but Massoud Ibrahim, a soft drinks vendor who saw the attack, said rocket-propelled grenades were fired at an American truck and armored vehicle.

Insurgents also fired a rocket-propelled grenade at a helicopter that arrived after the attack but missed, he said. The helicopter was unable to land. An armored vehicle was seen being towed away.

On Saturday night in Mosul, 240 miles north of Baghdad, three soldiers were wounded in an ambush by guerrillas who bombarded them with hand grenades from the top of a building. One soldier had his leg amputated after the attack, while the other two soldiers were wounded less seriously in the legs by shrapnel.