Iraqi delegates delivered a peace proposal to aides of Muqtada al-Sadr (search) in Najaf on Tuesday, but the militant cleric refused to meet with them as explosions, gunfire and a U.S. air strike on the sprawling cemetery echoed across the holy city.

The delegation was kept waiting for three hours at the Imam Ali (search) shrine, where some of al-Sadr's fighters have holed up, but were not allowed to meet with the cleric and left Najaf after talking with his aides.

Al-Sadr did not show up because of the "heavy shelling from the planes and tanks of the U.S. forces," said an aide, Ahmed al-Shaibany.

Both the mediators and Al-Sadr's deputies described their talks as positive. Al-Shaibany said the delegation would return Wednesday to meet with al-Sadr himself. Delegate Rajah Khozi said she hoped the group would be able to return Wednesday or Thursday, but there were no immediate plans for such a trip.

The peace mission was organized by the Iraqi National Conference (search), a gathering of more than 1,000 religious, political and civic leaders that was extended late Tuesday into a fourth day because of disagreements over how to elect a council that is to act as a watchdog over the interim government until elections in January.

The delegation's peace initiative demanded that al-Sadr's Mahdi Army (search) militia disarm, leave the Imam Ali shrine and become a political group in exchange for amnesty.

"This is not a negotiation. This is a friendly mission to convey the message of the National Conference," said delegation head Hussein al-Sadr, a distant relative of the renegade Shiite Muslim cleric.

Al-Sadr aides said they welcomed the mission, but not the peace proposal.

"The demands of the committee are impossible. The shrine compound must be in the hands of the religious authorities. They are asking us to leave Najaf while we are the sons of Najaf," said one aide, Sheik Ali Smeisim.

The delegation, which had planned to be in Najaf only for a day, flew back to Baghdad to return to the National Conference.

The fighting in Najaf, especially near the revered Imam Ali shrine, where al-Sadr's militants are holed up, has angered many among the country's majority Shiite population and cast a pall over the conference, which had been intended to project an image of amity and inclusiveness on the road to democracy.

The meeting is being held under tight security and two nearby explosions rattled the meeting hall Tuesday, slightly wounding a soldier and a civilian security guard, the military said.

Several miles away, a mortar round slammed into a busy Baghdad commercial district, killing seven people and wounding 47, officials said. The blast charred cars and shattered the front of a barbershop on al-Rasheed street, leaving blood mixed with glass and metal shards on the road.

The mortar shell was not aimed at the conference but rather was a routine attack intended "to create chaos in the country," said Sabah Kadhim, a spokesman for the Iraq's Interior Ministry.

In volatile Anbar Province, a Marine with the 1st Marine Expeditionary Force was killed in action Tuesday during "security and stability operations," the military reported. The Marine's name was being withheld until relatives could be notified.

In eastern Baghdad, insurgents attacked U.S. troops with rocket-propelled grenades and bombs Monday, killing one U.S. soldier and wounding several others, the military announced Tuesday.

Al-Sadr militiamen also fought a series of gunbattles with British troops in the southern city of Basra, with one British soldier and one militant reported killed. Sixty-five British soldiers have died since the start of the Iraq war.

In the volatile city of Fallujah, a U.S. warplane fired a missile at a house, killing two people and injuring one, said Dr. Adel Mohammed Moustafa of Fallujah General Hospital. The U.S. military had no immediate comment.

The 16-month-old insurgency, marked by car bombings, ambushes, kidnappings, sabotage and other attacks, has kept the country unstable and badly hampered reconstruction efforts.

But the latest round of fighting in Najaf, which began Aug. 5 after the breakdown of a two-month cease-fire, is presenting the greatest challenge yet to interim Prime Minister Ayad Allawi's fledgling government.

Clashes persisted even after the National Conference's eight-member peace delegation — seven of them Shiites — arrived aboard a pair of U.S. Army Black Hawk helicopters Tuesday afternoon.

Explosions and gunfire shook the streets throughout the day and U.S. troops entered the flash-point Old City neighborhood, where al-Sadr's Mahdi Army is based.

A U.S. warplane caused an explosion in the huge cemetery, site of many clashes between U.S. forces and Shiite militants. U.S. Marine Lt. Col. Thomas V. Johnson said the plane fired "one precision guided missile on a building in the cemetery where Muqtada militiamen with RPGs were attacking U.S. soldiers."

The U.S. military says the fighting in Najaf has killed hundreds of militants, though the militants deny that. Eight U.S. soldiers and at least 40 Iraqi police have been killed as well.

The fighting Tuesday killed three civilians and wounded 15, rescue worker Sadiq al-Shaibany said. Two of those were killed when gunfire hit the office of the Badr Brigades, the militant wing of the Supreme Council for the Islamic Revolution in Iraq, a Shiite political group that is not involved in the fighting, said Ridha Taqi, an official of the group.

The National Conference, originally scheduled to end Tuesday, was extended to Wednesday because of a dispute over how to elect members of the Iraqi National Council, which is to serve alongside the interim government.

The delegates were originally to vote on one slate of 81 potential members, which would have had to garner 65 percent of the vote to become part of the new council. However, some smaller parties felt they did not have enough of a voice in the makeup of the slate, organizers said.

As a compromise, several slates will contend with each other Wednesday, with the top two moving into a runoff, where the winning slate will become part of the council.

"The most important thing here is balance, that there's balance at this critical stage that we are in," said conference chairman Fuad Masoum.

The final 19 seats of the 100-member body will be filled by members of the former U.S.-appointed Governing Council who were not included in the interim government.

In other developments Tuesday:

—An unmanned U.S. reconnaissance plane crashed, the military said. It was not known what caused the U.S. Air Force MQ-1 Predator to go down near a U.S. base in Balad, 50 miles north of the capital.

—Al-Sadr militants attacked U.S. patrols in Baghdad's Sadr City neighborhood, sparking gunbattles Tuesday evening, U.S. Army Capt. Brian O'Malley said. There were no immediate reports of casualties.

—In Basra, in addition to the clashes involving British troops, al-Sadr militants also attacked a pair of civilian cars reportedly carrying Britons, destroying the vehicles and wounding two people, police Col. Kareem Sadkhan said. He said those inside the vehicles exchanged fire with the militants, wounding one and a bystander.