Members of the new Iraqi National Guard ventured into a tough neighborhood of Baghdad on Wednesday to show that they did not need U.S. troops to keep the peace. Their first test came quickly. Grenades rained down from the roofs of high-rise buildings and automatic gunfire spit at them from every direction, the guardsmen said.

"It was a battlefield," said one of the guardsmen, who was shot in the leg. "Even when the Americans came into Baghdad, there wasn't resistance like this."

The gunfight, which sent booms rattling through downtown streets, killed four people and wounded 27, officials said. Hours earlier, a mortar attack on an exclusive neighborhood in west Baghdad, near a residence of Iraq's interim prime minister, Ayad Allawi, wounded six civilians. And in another area downtown, police disarmed a large car bomb.

The mortar attack came just hours before Allawi was scheduled to announce tough new security measures to help battle insurgents. Allawi, whose home was not hit, called the attack "cowardly."

The firefight involving the guardsmen began about 10 a.m. as they were forming patrols to enter the Utafiyah neighborhood, on the west bank of the Tigris River along Haifa Street, a busy commercial area. It is a difficult neighborhood, but the guardsmen said they did not expect violence.

"This was the first time our National Guard unit was going in there to set up checkpoints and guard the neighborhood," Staff Sgt. Jalal Taha, 34, said from a hospital bed where he was recovering from a bullet wound to his foot and smoking a cigarette. "We wanted to go alone, without the Americans. The whole battalion was out today to show people there is security and we can provide it without the Americans.

"My group had about 30 soldiers. At the moment we got in the neighborhood, they attacked us from the roofs" of a cluster of seven-story apartment buildings. "Grenades came down from all four buildings around us. We could see them on the rooftop. We could see them on the balconies, throwing grenades and shooting. We fired back, and then it seemed like all the buildings started to attack us."

"They were hiding in the apartments," Staff Sgt. Abbas Hussein said. "They used small arms, hand grenades and then rockets and mortars."

Another guardsman, Amar Ghassan, 19, said the attackers threw a grenade down the stairwell of a building as he raced up to confront them. He said he ducked into a room for shelter.

"I couldn't go back out the same way, so I had to break a window to get out," Ghassan said. He said he gashed his arm on the glass.

Marwan Ghalib, 38, an architect, drove to the area after the shooting began so he could pick up his mother-in-law from her job as a school administrator. "A policeman warned me not to go there, but I said, 'Let's leave it to God,' " he said. But his mother-in-law had already left. As Ghalib returned to his car to drive away, he said, mortar shells hit 10 yards away, sending shrapnel into one of his legs, his back and his head. He ran to the car, he said, and drove himself to the hospital.

Kamal Ali, an ambulance driver at Khark Hospital, said that when he heard people had been wounded in the fighting, he raced to the nearby neighborhood.

"It looked like a battlefield with explosions and shooting," he said. "I could feel the bullets go near me. I picked up one soldier after another -- six wounded in all. I don't know how I had the strength, but I just piled them in together in my ambulance and raced out."

Ali Saad, 23, a taxi driver, said he saw gunmen pump two bullets into the head of a guardsman lying in the street. The attackers videotaped the scene as the body was dragged through the street, Saad said.

"These were Iraqis," Saad said. "I was close enough. I could hear their dialect."

Hospital officials said four people were killed: a guardsman, a policeman and two civilians. Ten civilians and 17 guardsmen and police officers were injured. Officials said it was unclear whether any of the insurgents were among the injured.

According to a U.S. military spokesman, police called for backup after a station was hit. U.S. armored vehicles entered the neighborhood and helicopters roared overhead.

A U.S. Army rapid response team entered the area on foot and patrolled cautiously as aircraft radioed the position of the gunmen. Several soldiers became ill from dehydration in the 112-degree heat.

The U.S. soldiers came to back up the Iraqis but withdrew when it became clear that "the Iraqi National Guard was handling the situation. The Iraqis had things under control," a top U.S. military officer said on condition of anonymity. "While there still may be casualties and loss of life, the direction we are headed is of having Iraqi security forces take care of security."

A military spokesman said the U.S. soldiers did not fire and had no casualties.

But Sgt. Taha said the situation was not under control.

"We were just trying to withdraw. I ordered my men to stop shooting in hopes that the other side would let us withdraw. We were hiding by the walls and kept backing up until we got out.

"As we were going out, I felt my foot wasn't moving. I looked and saw a hole in my boot and blood coming out. I knew I was shot. Two of my colleagues carried me out."

"I was 17 years in the old army," Taha said. "I never saw anything like this."

Meanwhile, al-Jazeera television broadcast a videotape of armed men holding a Filipino hostage and threatening to kill him if the Philippines does not withdraw its small force from Iraq in three days, the Associated Press reported. The previously unknown group, the Iraqi Islamic Army-Khaled bin al-Waleed Corps, claimed to have already killed an Iraqi security guard who was accompanying the man, the newscaster said.

The videotape displayed a company card identifying the hostage as Hafidh Amer of the Philippines. No details of his capture were given.

Staff photographer Andrea Bruce Woodall contributed to this report.

A U.S. soldier is treated for heat exhaustion during a mission to aid Iraqi guardsmen attacked by insurgents during a patrol in Baghdad.