BAGHDAD, Iraq - Insurgent bombers killed three Iraqi national guardsmen, a police chief and a patrolman today in the militants' unrelenting attacks against the country's security forces.

Also, two U.S. 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 today from his wounds.

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

A truck bomb targeted a police recruiting center last week in Baqouba, 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 U.S. Army spokesman.

In today's first bomb attack, pictures from western Baghdad's al-Washash district showed a destroyed white Iraqi police pickup truck, its doors smashed and blood splattered on the inside.

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, U.S. forces fought Monday with gunmen protecting radical Shiite cleric Muqtada al-Sadr's house in clashes that killed one woman and wounded three people.

At least six U.S. 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 U.S. forces withdrew, witnesses said.

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

Ali al-Yassiry, a Baghdad spokesman for al-Sadr, said U.S. 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 U.S. 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 U.S.-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 arrest warrant was postponed.