Late Sunday, U.S. journalist Micah Garen, who was kidnapped Aug. 13 in the southern city of Nasiriyah, was released along with his Iraqi translator at al-Sadr's offices there after the cleric's aides appealed for his freedom.
Garen and his translator, Amir Doushi, were walking through a market when two armed men in civilian clothes seized them, police said. Insurgents later released a video of Garen and threatened to kill him if U.S. troops did not leave Najaf.
In a brief interview with the pan-Arab television station Al-Jazeera after his release, Garen thanked al-Sadr's representatives for their work, which included an appeal to the kidnappers during Friday prayers.
Sheik Aws al-Khafaji, an al-Sadr aide, said the kidnappers mistakenly had thought Garen was working for the U.S. intelligence services.
"The kidnappers listened to the call that we made during Friday prayers, and they contacted us and we asked them to bring him to (al-Sadr's) office and promised that no one would pursue them," al-Khafaji said.
Four Marines from the 1st Expeditionary Force were killed in separate incidents in Anbar province - which includes the Sunni hotbeds of Fallujah and Ramadi.
Near Mosul, one soldier died today when the convoy he was traveling in was hit by a roadside bomb.
Their deaths bring to 957 the number of US troops killed in Iraq.
Explosions and gunfire shook Najaf's Old City on Sunday in a fierce battle between U.S. forces and Shiite militants, as negotiations dragged on for the handover of the shrine that the fighters have used for their stronghold.
Late Sunday, U.S. warplanes and helicopters attacked positions in the Old City in Najaf for the second night with bombs and gunfire, witnesses said. Militant leaders said the Imam Ali Shrine compound's outer walls were damaged in the attacks.
The U.S. military, which has been careful to avoid damaging the compound, said it fired on sites south of the shrine, where militants were shooting from, and did not hit the compound wall.
Sunday's clashes in Najaf appeared more intense than in recent days as U.S. forces sealed off the Old City. But Iraqi government officials counseled patience, saying they intended to resolve the crisis without raiding the shrine, one of Shia Islam's holiest sites.
"The government will leave no stone unturned to reach a peaceful settlement," Iraqi National Security adviser Mouaffaq al-Rubaie told The Associated Press. "It has no intention or interest in killing more people or having even the most trivial damage to the shrine. We have a vested interest in a peaceful settlement."
Senior government officials said last week an Iraqi force was preparing to raid the shrine within hours to expel the militants loyal to radical Shiite cleric Muqtada al-Sadr, but interim Prime Minister Ayad Allawi quickly backed off that threat.
Such an operation would anger Shiites across the country and could turn them against the new government as it tries to gain legitimacy and tackle a 16-month-old insurgency.
In the Anbar province, the heart of the Sunni insurgency, four U.S. Marines with the 1st Marine Expeditionary Force were killed in separate incidents, the military announced Sunday.
One Marine was killed in action Saturday and two others died Saturday of wounds received while conducting "security and stability operations" in the province, the military said. Another Marine was killed Saturday when his Humvee flipped after running into a tank, the military said.
A roadside bomb attack Sunday targeting a U.S. military convoy outside the northern city of Mosul killed one U.S. soldier assigned to Task Force Olympia and wounded another, the military said. The injured soldier was in stable condition. Two Iraqi children also were injured in the blast, said Dr. Mohammed Ahmed of al-Jumhuri hospital.
As of Friday, 949 U.S. service members have died since the beginning of military operations in Iraq in March 2003, according to the U.S. Defense Department.
In Najaf, U.S. tanks rumbled down deserted streets Sunday, while sporadic gunfire filled the air. The roads leading to the shrine were muddied and filled with chunks of concrete ripped from the streets. Black smoke trailed from a building, as the clatter of automatic gunfire rang out.
In the afternoon a fierce battle between the military and al-Sadr's militants broke out when insurgents launched a mortar barrage at U.S. troops, witnesses said. Calm returned to the city after about half an hour.
U.S. forces sealed off the Old City, the center of the more than two weeks of fighting here, restoring a cordon that had been loosened in recent days.
Several mortar attacks targeted police offices in the city, but no one was injured, officials said.
Early Sunday, U.S. warplanes bombed the Old City and the sounds of shelling could be heard in the streets, witnesses said. The U.S. military could not confirm the bombing.
At least three people were killed and 18 injured during overnight fighting, said Tawfiq Mohammed of Najaf General Hospital.
Fighting in the nearby city of Kufa on Saturday killed 40 militants, according to the Interior Ministry. However, Mahmoud al-Soudani, an al-Sadr aide, called the claim "government propaganda" and said only one militant had been killed.
Al-Sadr himself has not been seen in public in days, but al-Soudani said the cleric was in good health and remained in Najaf.
The crisis in Najaf, which has spread to other Shiite communities, appeared on the verge of resolution Friday, when insurgents agreed to turn over the shrine to representatives of Iraq's top Shiite cleric, Grand Ayatollah Ali al-Husseini al-Sistani.
But the transfer has bogged down amid quibbling over technicalities. Representatives from both sides said Sunday they were still working out the details.
Al-Rubaie said the government was willing to wait while the two sides worked out an agreement on the shrine, but added that al-Sadr needed to dismantle his Mahdi militia as well to end the violence.
"He has to show definite signs that he agrees, whether going on television or signing an agreement promising that he will disband the army," he said. "It's very important. We cannot live in a peaceful, democratic country with a militia."
Also Sunday, Polish Defense Minister Jerzy Szmajdzinski paid a visit to his troops in Iraq and said the persistent attacks here would not deter Poland from fulfilling its commitments.
Attending a memorial Mass for a Polish soldier killed in a bombing Saturday, he said: "Let us make a vow that his death will not be in vain, that we will go on with our mission." Poland has about 2,400 troops in Iraq.
In other violence Sunday:
A suicide attacker detonated a car bomb alongside the convoy carrying a deputy provincial governor, Bassam al-Khadran, in the town of Khalis, north of Baghdad. The blast killed two people and injured 14 others, including al-Khadran, Iraqi officials said.
In Jur al-Nadaf, 12 miles south of Baghdad, attackers sprayed a police vehicle with machine-gun fire, killing two policemen before fleeing, said Col. Adnan Abdul-Rahman of the Interior Ministry.
In Mosul, 225 miles northwest of Baghdad, gunmen opened fire on a car, killing an Indonesian citizen and injuring a Filipino, hospital officials said. Two Iraqis, the car's driver and a bodyguard, were also killed in the attack, Dr. Dhia Taha said.
In the southern city of Basra, an Iraqi intelligence officer kidnapped nearly a week ago and threatened with death if U.S. and Iraqi forces did not end the violence in Najaf was found dead, his body riddled with bullets, police said Sunday.