Also, two US soldiers were killed and two others wounded by a roadside bomb late Monday in Iraq's capital, while two American Marines died of wounds received in fighting in Anbar Province west of Baghdad, the military said. One of the Marines died during the Monday engagement; the second died Tuesday from his wounds in that fighting.

Meanwhile, four Iraqis working for a French aid group in the southern city of Samawa were stabbed to death while travelling by car to Najaf further north, their employer and families said yesterday.

The Paris-based Agency for Technical Cooperation and Development (ACTED) confirmed by telephone that four of its workers were killed in Iraq but declined to provide further details.

The national guardsmen were killed when a car bomb hit their post north of Baquoba. Four guardsmen were wounded, the US military said.

A truck bomb Wednesday targeted a police recruiting center in Baqouba, 35 miles northeast of Baghdad, where hundreds of job applicants were gathered. It killed 70 people.

"The continued targeting of Iraqi security force personnel ... undermines the security of all Iraqis and will only quicken the resolve of Iraqi security forces to provide a safe and secure environment," said Maj. Neal O'Brien, a US Army spokesman.

In yesterday's first bomb attack, Associated Press Television News pictures from western Baghdad's al-Washash district showed a destroyed white Iraqi police pickup truck, its doors smashed and blood splattered across the driver's seat.

Police, speaking on condition of anonymity, identified one of the dead Iraqi officers as Col. Mouyad Mohammed Bashar, who was chief of al-Mamoun police station.

A third officer was wounded in the blast, said Zayed Mohammed, a doctor at al-Yarmouk hospital. At the hospital, a bloodied policeman lay on a bed, bandages wrapped around his stomach and leg.

Police in Iraq have repeatedly been targeted by insurgents pressing a campaign to destabilize the interim government. The guerrillas see police as collaborators with American coalition forces.

From April 2003 to May 2004 alone, 710 Iraqi police were killed out of a total force of 130,000 officers, authorities said.

In the holy city of Najaf, US forces fought yesterday with gunmen protecting radical Shia cleric Muqtada al-Sadr's house in clashes that killed one woman and wounded three people. The US military had no immediate comment.

At least six US military vehicles entered the Zahra area in Najaf near al-Sadr's house, which is protected by his militia, the Mahdi Army, witnesses said.

Barrages of gunfire and mortar rounds set cars on fire before Iraqi police intervened and the US forces withdrew, witnesses said.

"One woman was killed and we have three injured," said Ajwak Kadhim, director at Al-Hakim Hospital in Najaf, 100 miles south of Baghdad.

Ali al-Yassiry, a Baghdad spokesman for al-Sadr, said US troops briefly surrounded al-Sadr's house in Najaf but then withdrew from the city. He said the fighting ended and the Mahdi Army was patrolling the area.

Al-Sadr, who is wanted by US forces for the April 2003 murder of a moderate cleric in Najaf, was in his house at the time, witnesses said.

The radical cleric, who has grassroots support for his anti-coalition stance, began a two-month rebellion in early April after the US-led occupation authority closed his newspaper and arrested a key aide. A series of truces ended the fighting, and the issue of whether to carry out his the arrest warrant was postponed.

In northern Iraq, saboteurs bombed an oil pipeline northeast of the town or Beiji yesterday in the latest attack on the nation's infrastructure, the US military said.

Police Col. Nurzad Ahmed, a security official at the state-run Northern Oil Company, said a fire was raging near al-Fattah, about 135 miles north of Baghdad, but the pipeline, which was not an export line, was not on fire. He said a nearby trash heap had been set ablaze.

"The fire is huge and we have started our efforts to put it out," Ahmed told The Associated Press.

Maj. Neal O'Brien, a spokesman for the US Army's 1st Infantry Division, said the fire had spread to a nearby construction site.

It was unclear what effect, if any, the explosion would have on oil exports. Insurgents have repeatedly attacked Iraq's oil infrastructure in an effort deprive the interim government of money for reconstruction efforts.

In Baghdad, insurgents set off a roadside bomb late Monday, killing two US soldiers and wounding two more, the military said Tuesday.

The Marine's killing brought to at least 915 the number of US service members who have died since the beginning of military operations in Iraq.