Three U.S. soldiers were killed late Wednesday and early Thursday in two separate Baghdad attacks while in the south of Iraq, U.S. troops were reported to be fighting the militia loyal to radical cleric Moqtada Sadr on the edges of the city of Najaf.

Lt. Col. Pat White, in a live interview with CNN, said Army units had retaken the governor's office in Najaf, which had previously been under the control of Sadr's militiamen, known as the Mahdi Army.

The U.S. strategy in Najaf is to "chip away" at Sadr's forces, and create "greater space" for local Shiite leaders to increase pressure on the cleric, said a senior U.S. official in Washington involved in Iraq policy.

The official, who insisted on anonymity in order to speak more candidly about U.S. objectives, said the "goal is to chip away" at Sadr's support and show Shiite leaders in Najaf "that Sadr does not and will not have a power base."

"The intent is to encourage prompt Iraqi action," the official said. " . . . They need to stand up to this guy. When we start to see the snowball effect of the erosion of Sadr's support, that gives us greater space to take military action."

"Ideally, if we take the governor's house and some of his supporters, it gives our nominal allies among the Iraqis more space to act. It's a lot better than going in with tanks," he added.

Fighting east of Najaf killed an estimated 40 members of the militia around Kufa Thursday, Capt. Roger Maynulet, commander of a tank company with the Army's 2nd Armored Cavalry Regiment, told the Associated Press.

U.S. officers said American forces were sent to areas east of the city to draw militia fighters away from the governor's office, which was taken without a fight, the AP said.

There was no sign that U.S. troops were entering the heart of Najaf, which is sacred to Shiite Muslims and has been encircled by U.S. forces since early April.

The U.S. administrator in Iraq, L. Paul Bremer, announced that he was appointing a new governor for Najaf. According to a transcript of the announcement, Bremer said Adnan Zurufi would take office immediately, replacing Haider Mayali, who left the country for Iran.

"He is the right man for the job at this time . . . ," Bremer said, referring to Zurufi's past work seeking to unseat former Iraqi leader Saddam Hussein. "Governor Zurufi's attachment to Najaf and his proven willingness to fight for justice will serve the people well as he administers the government."

In Baghdad, two U.S. soldiers died and two were wounded as a result of an improvised bomb attack just before midnight, a military spokesman announced. No further details were available.

At 7:30 a.m. (11:30 p.m. EDT) a massive suicide car bomb exploded near a checkpoint leading to the headquarters of the U.S. occupation authority in Baghdad.

The blast killed one soldier and at least five Iraqi civilians while injuring at least two dozen Iraqis, a U.S. military spokesman said. Witnesses at the scene said the bomber was among those killed.

The explosion destroyed several vehicles and sent black smoke billowing over the city during the morning rush hour as helicopters, Army Humvees and Bradley Fighting Vehicles cordoned off the area.

Witnesses said the suicide bomber was driving a white Toyota and that the driver made three passes past the checkpoint before speeding toward the U.S. troops manning it. The checkpoint is at the 14th of July Bridge, which leads into the fortified Green Zone where the occupation authority works.

Each morning Iraqis who work for the Coalition Provisional Authority line up to go through this checkpoint to jobs either in construction or cleaning. The driver blew himself up right beside a line of these workers.

"They threatened the laborers in this neighborhood," said Hussein Ali, 24, who was at the scene of the bombing looking for two cousins and brothers who headed to work 15 minutes before the blast. "If they do this work, they will kill them."

Ali said that members of Sadr's militia have been threatening people orally and distributing pamphlets to people who live in his neighborhood and work for the U.S. occupation authority. He said his brother, who works as a cleaner inside the Green Zone, told him he had even been threatened by other Iraqis working inside the coalition headquarters.

Shopkeepers swept up their shattered windows within a block of the blast. "All these people killed and injured and they have families to support," said Hassan Abed, 20, who is unemployed and lives in the neighborhood. He said that when he heard the explosion, "my heart fell down."

In other developments, the Dubai-based al-Arabiya satellite television networked showed video of a blindfolded man, described as an Iraqi-American hostage in Iraq, pleading for help.

The man, speaking in English, said he worked with the Pentagon as a civilian engineer. The man, who said he was kidnapped May 3, appealed to international agencies to win his release. He did not identify his kidnappers in the brief segment that was aired.

Al-Arabiya television said it received the tape Thursday. It did not say how or where it was received, the AP reported.

Dozens of foreigners have been kidnapped in Iraq recently. Some have been released and others killed by their captors.

Revelations about the abuse of Iraqi prisoners held by U.S.-led occupation forces continued to produce reaction in the Middle East Thursday, as the International Committee of the Red Cross said it had been aware of the situation in the Abu Ghraib prison near Baghdad and had spoken with American officials repeatedly about it.

"We are not surprised at what is coming out," said Nada Doumani, the Red Cross' Jordan-based spokeswoman. In a phone interview, she said the humanitarian organization began alerting officials in November following an October visit to the facility.

She said the Red Cross submitted another report to the head of the facility in February after another inspection.

"We have repeatedly asked them to take corrective action. I think they took our remarks very seriously and took some action," she said, declining to go into detail.

The Washington Post reported in Thursday's editions that State Department officials have been particularly concerned about what they said was the Pentagon's reluctance to heed urgings from the Red Cross to improve conditions at Iraqi prisons.

Wright and Barbash reported from Washington.