BAGHDAD, Iraq – U.S. warplanes pounded away at followers of radical cleric Muqtada al-Sadr in Najaf and tanks advanced closer to the shrine where the rebels have gathered, as Iraq’s interim government warned Sunday night that a raid on the mosque is imminent.

Also Sunday, five U.S. service members died in separate incidents across Iraq and a kidnapped American journalist was released by his captors.

Iraqi Minister of State Kasim Daoud summoned reporters to the prime minister’s villa inside the secure Green Zone and announced that the government was a “few hours” from starting military action to oust militia members from the Imam Ali mosque.

Al-Sadr’s followers have been holed up there since Aug. 5.

“We mean it, and still we are counting the hours,” Daoud said, urging al-Sadr to evacuate his followers from the mosque and accept a demand that his militia disarm.

But it was unclear how soon an attack on the mosque might be.

With the young Shiite cleric and the fledgling government locked in a test of wills, each has alternated between tough talk and gestures of conciliation. The government has twice before announced a raid was hours away, only to back down.

The protracted standoff challenges the legitimacy of the interim Iraqi regime. But an attack on the shrine risks provoking a broader uprising among Iraq’s majority Shiite population. The mosque is one of Islam’s holiest sites, containing the burial place of Ali, the son-in-law of the Prophet Muhammad and a figure especially revered by Shiites.

Amid heavy bombardment of the Old City near the mosque early Sunday and fighting Saturday in nearby Kufa, 49 people were killed and 27 wounded in Najaf province between Saturday and Sunday mornings, according to the Iraqi Health Ministry.

It was not clear how many of the casualties were militia members and how many were civilians.

An unofficial mediator and distant relative of al-Sadr’s urged the cleric to accept the government’s conditions.

“We are in a race with time,” said Hussein al-Sadr, who led a peace delegation to Najaf last week.

The cleric’s representatives accepted the delegation’s peace plan. But the process has unraveled amid disagreements with religious authorities involving a hand-over of the shrine.

Al-Sadr’s followers have said they would hand the keys to the shrine to representatives of Grand Ayatollah Ali al-Sistani but would retain “custody” of the holy place.

Representatives of the cleric also say they want religious authorities to inventory the shrine’s treasures before custody of the mosque shifts so that militia members cannot be accused of stealing any of the precious gifts brought by pilgrims over the years.

But as long as there are weapons in the shrine, al-Sistani’s representatives have said they would not approach the mosque.

After aides to al-Sadr pleaded for the release of U.S. journalist Micah Garen, he was set free late Sunday.

Garen was abducted in the southern city of Nasiriyah as he and a translator were walking through a market. Garen was working on a documentary about looting at archaeological sites in the city.

In a brief interview on Al Jazeera, Garen thanked al-Sadr’s representatives for their work on his behalf. He was turned over to Sadr’s office in Nasiriyah and set free there.

An Italian journalist and two French journalists also have been reported missing in recent days.

In Western Iraq’s volatile Anbar province, which includes Fallujah and Ramadi, four U.S. Marines died Sunday. One was killed in action and the others died of wounds received in separate incidents Saturday.

Outside the northern city of Mosul, one U.S. soldier died and another was wounded when a roadside bomb exploded as a military convoy passed, the military said. A local doctor told The Associated Press that two Iraqi children also were injured in the blast.

At least 958 U.S. service members have died in Iraq since the beginning of military operations in March 2003, according to the U.S. Defense Department.

In Khalis, north of Baghdad, a suicide bomber detonated a car bomb beside a convoy carrying a deputy provincial governor, Bassam al-Khadran. The official was wounded and two of his bodyguards were killed.