An American soldier was killed and five were wounded early Thursday when they were hit by a rocket-propelled grenade, the U.S. military said -- the latest attack in a tense city where resistance against American occupation has been vocal and sometimes violent.

Scores of U.S. Army military police sealed off the area and launched house-to-house searches for the assailants. Residents said the attack, at an American checkpoint in front of a police station, left "blood everywhere."

The assault came a day after more than 1,500 soldiers from the U.S. Army's 3rd Infantry Division (search-- which helped fight the war and take Baghdad -- moved into Fallujah (search) and surrounding areas in central Iraq. Their mission is to quell increasing attacks on U.S. occupying forces in the region.

Jamal Hussein Ali, 27, said he saw the immediate aftermath of the nighttime assault, which he said began with small-arms fire at around 12:30 a.m. Thursday.

"Then we heard an explosion," Ali said. "We saw the American troops shooting and running. They crossed the street, broke down a shop door and took cover inside."

The Army soldiers who came under fire were assigned to the 3rd Armored Cavalry Regiment of the 101st Airborne Division (search), the military said in a statement. That regiment has been based in the area for weeks.

The wounded soldiers were evacuated to a nearby military field hospital. Their identities weren't immediately released.

"They finished a dismounted patrol and they were preparing to leave, and they were getting on their vehicles to leave, when they were engaged in what I think was an RPG attack," said Lt. Col. Toby Green of the 3rd Armored Cavalry, which has about 300 soldiers in the area.

The attacker was an "unknown assailant," according to the military statement. It did not say if any Iraqis were killed or wounded in the ensuing battle. Weapons were found in a search of the area after the incident, Green said.

Fallujah has been a flashpoint of resistance to American occupation, and U.S. forces have come under increasing attack in the area, about 30 miles west of Baghdad. Senior military commanders acknowledge the resistance but say they believe it is not coordinated.

"There's still resistance here, that's true," Green said. "It is fair to say there is not enough security here yet. The safety and security of the town needs to improve if any kind of rebuilding process is going to continue and accelerate."

The commander of U.S. ground forces in Iraq, Lt. Gen. David McKiernan, said Wednesday that the spate of attacks in and around Fallujah was a last-ditch effort by Saddam supporters.

"I don't see any pattern of centralized command and control over these incidents," McKiernan said.

Anger in Fallujah grew in late April after confrontations between residents and American forces left 18 Iraqis dead and at least 78 wounded. Residents have accused U.S. troops of using excessive force and of not respecting Islamic practices.

On Wednesday, forces from the 3rd ID moved into Fallujah and the nearby city of Habaniyah in a high-profile show of force. The rocket-propelled grenade attack took place just hours later.

By Thursday afternoon, military police attached to the 3rd ID had blocked off streets and moved from house to house in the area around the police station, on a main street. They rousted residents and ordered them to leave by using amplified messages in Arabic from Humvee-mounted loudspeakers.

"The coalition is involved in a dangerous operation," the announcements said. "For your safety, you must evacuate this area. Stay off the streets or you'll be hurt or wounded."

At least one man was handcuffed and taken away -- apparently for possessing an illegal weapon, U.S. forces at the scene said. Military police also photographed gathered crowds -- a standard intelligence-gathering tool after an attack.

Ali, recalling the minutes after the assault, said four tanks, four Humvees and three Bradley Fighting Vehicles quickly arrived as backup. "There was blood everywhere," he said.

Mustafa Daoud, 18, heard shooting just past midnight "all around the Americans."

"We saw them running," he said.

Before this latest incident, the 3rd Armored Cavalry Regiment, based in Fort Carson, Colo., had already lost three soldiers in the past two weeks.

Staff Sgt. Michael B. Quinn, 37, and Sgt. Thomas F. Broomhead, 34, were killed May 27 in a firefight in Fallujah. Maj. Mathew E. Schram, 36, died May 26 when a convoy was ambushed 120 miles north of Baghdad.