U.S. Marines, hunting for Iraqi leaders believed to be meeting nearby, engaged in a heavy firefight Thursday with Iraqis holed up in a mosque. Warplanes also targeted Saddam Hussein's half brother as U.S. forces continued their attempts to finish off Iraq's leadership.

U.S. Central Command spokesman Frank Thorp said he did not know if Saddam was among those thought to be at the meeting. But The Washington Post reported on its Web site Thursday night that the Marines were acting on a tip that Saddam and his younger son, Qusai, were hiding in the area.

Though Saddam's hold on Baghdad had crumbled, the mosque battle was just one sign that the war was hardly over: A suicide attacker set off a bomb, wounding four Marines, and Iraqi artillery shells apparently hit an Army-held compound.

U.S. troops were also ordered to put a stop to looters who have run wild in the capital amid celebrations over Saddam's fall. The 7th Marine Regiment planned to enforce a dusk-to-dawn curfew beginning Friday evening in the area it patrols in eastern Baghdad.

Marines battled Iraqi fighters in and around the Imam al-Adham Mosque in northern Baghdad for seven hours until they captured the mosque. One Marine was killed and 22 others wounded. U.S. Central Command said the18 Iraqis were captured along with weapons and explosives.

The Marines had been tipped that Iraqi leaders were holding a meeting at a Baath Party official's home near the mosque and near the al-Azimiyah Palace when they came under fire from the mosque area.

U.S. officials had received reports that a wounded Saddam was hiding in the house near the Imam al-Adham Mosque, according to a New York Times reporter. Neighbors in the area told the reporter that they had seen Saddam greeting a throng of supporters as he paid a visit to the mosque on Wednesday. One man said he even kissed the Iraqi leader's feet.

Before dawn Friday, warplanes fired six satellite-guided bombs at an intelligence building in Ramadi, a town 60 miles west of Baghdad, believing that Saddam's half brother, Barzan Ibrahim al-Tikriti, was inside.

Al-Takriti, a former head of the secret police, is a close adviser to Saddam and allegedly helped hide millions of dollars abroad while ambassador to Switzerland. U.S. Central Command said it was still assessing damage and casualties from the strike.

Since the war's first day, U.S. forces have been aiming to decapitate the regime, though the results have been uncertain. Saddam apparently survived a strike against him on the first night of bombing; on Monday, warplanes leveled a Baghdad building where they believed the Iraqi president was located, though there's been no confirmation. A strike the same day in the southern city of Basra is thought to have killed Saddam's cousin, Ali Hassan al-Majid, a top military commander.

Reveling in the capital's power vacuum, looters were out for a second day Thursday, lugging away furniture, appliances and armloads of light bulbs.

Dismayed by the pillaging of al-Kindi hospital Wednesday, medical students fanned out in the neighborhood to demand the return of medicine and other supplies. Garbed in blue hospital smocks, they returned cheering triumphantly in double-decker buses filled with boxes.

In the sprawling Saddam City district, a Shiite Muslim cleric, Amar al-Saadi, said some residents of the poor area had set up roadblocks and were confiscating looted items. The goods were being stored at a mosque, he said.

Officers in the 7th Marine Regiment said they received orders Thursday night to try to stop looting -- at their discretion.

Lt. Col. Michael Belcher, commander of the regiment's 3rd Battalion, said his priorities were first to protect key structures, such as the power system, and second to safeguard humanitarian sites like hospitals and aid distribution centers. Commercial buildings are last, he said.

"If I see them tearing down electrical infrastructure in some of these facilities, I'll step in to stop it," Belcher said. "What we found so far is that if you confront the looters, they'll put it down and go away."

Combat flared across Baghdad throughout the day.

About 7:30 p.m. Thursday, four Marines suffered serious wounds when a man strapped with explosives approached a U.S. checkpoint near Saddam City and blew himself up, said Capt. Joe Plenzler, a spokesman for the 1st Marine Division.

There was no immediate information on whether there were civilian casualties.

"We expected the enemy would try to pull all the dirty tricks out of the bag," Plenzler said, alluding to two previous suicide attacks on U.S. troops and the warning from Saddam's regime that suicide attacks would be "routine military policy."

An hour earlier, two explosions, apparently from artillery shells, caused several small fires at the southern end of the Old Palace compound in central Baghdad. U.S. soldiers occupying the site returned fire with tank cannons. There was no report of casualties.

The sound of a mammoth explosion rumbled across Baghdad late Thursday. Illuminated by the moon, a cloud could be seen from the center of town boiling hundreds of feet into the sky toward the north. There was no immediate word on what caused the blast.

Associated Press journalists who made it to the northwestern part of Baghdad found a near ghost town, with shops shuttered and streets empty of traffic. Small groups of Iraqi fighters manned sandbag positions and hid behind bushes. No U.S. troops were seen, except at one road intersection.

A visit to the nearby Russian Embassy, where rumors on Wednesday speculated Saddam might be hiding, found no signs of life. Two road barricades outside also were deserted.

Elsewhere in the city, people streamed out of government buildings with booty, piling it in wheelbarrows, donkey carts and battered pickup trucks.

"When I came down here earlier, I said, 'They're taking everything but the kitchen sink,'" Marine Staff Sgt. John Kelley, 29, of Toronto, Ohio said. At that moment, he looked around to see a man carrying just that. "Ah," Kelley said, "he's got a sink."

One boy in ripped rubber boots dragged a dilapidated electric ceiling fan down the street. A man driving a small Volkswagen pointed to his catch -- an obviously broken industrial air conditioner protruding from the tiny trunk.

Omar Amir ended up with a new mattress, poached from a government office. "I need one. I don't have one," he said, smiling broadly.

Some people shot big grins at American soldiers and Marines or put down their prizes to offer a thumbs-up or a quick finger across the throat and a whispered word -- "Saddam" -- before grabbing their loot and vanishing.

Some passers-by stopped to give flowers to Marine combat engineers guarding the Interior Ministry compound. "It's like all this was worth something now," said one guard, Kurt Gellert, 27, of Atlantic City, N.J.

U.S. soldiers intervened at one bank to disperse a throng that was trying to shoot open a safe with rifles. At a police academy across from the Interior Ministry, Marines kept looters away from an armory brimming with assault rifles, crates of mortar shells and grenades and scores of boxes of knives and pistols.

A woman, too frightened to give her name, said she hoped U.S. troops would restore order soon.

"We have all been surprised by the chaos," she said in English. "Everything is out of control. We can't sleep because we are afraid of being attacked by our own people."