Insurgents killed seven Iraqi security personnel in a car bombing and other attacks Tuesday, and the U.S. military announced the deaths of six Americans, including four killed by guerrillas.
The American dead included two soldiers killed by a roadside bomb and two Marines who died after being wounded in fighting Monday. Two others died in non-combat-related incidents. The U.S. deaths brought at least 919 the number of U.S. service members who have died since the beginning of military operations in Iraq.
Also Tuesday, saboteurs set off a bomb at a key northern oil pipeline, sparking a fire and sending huge plumes of thick black smoke into the sky. The explosion had no immediate effect on exports, which had been halted for weeks from the north.
Iraqi Prime Minister Ayad Allawi blames the continuing violence on "evil powers... trying to stop Iraq's march toward safety."
"We expect that as Iraq's (security) capabilities increase, the crushing of these (armed) operations will increase," Allawi told reporters Tuesday.
Meanwhile gunmen, apparently Sunni Muslims, shot Tuesday at an office belonging to the movement of Iraq's most senior Shiite cleric, Grand Ayatollah Ali al-Husseini al-Sistani, in the town of Yusifiya, about 15 miles south of Baghdad - an area of frequent insurgent attacks.
The Shiite residents shot back, killing six of the attackers and capturing three, according to Col. Anwar al-Ubaidi, police chief of the nearby town of Mahmoudiya.
In the city of Najaf, south of Baghdad, forces loyal to radical Shiite cleric Muqtada al-Sadr were holding 18 police hostage as leverage to force authorities to release their comrades, a police official said Tuesday on condition of anonymity.
The abductions reflected increasing friction that has threatened a fragile truce that ended two months of fighting that began in April between al-Sadr's Mahdi Army militia and U.S. troops. Marines and al-Sadr's militiamen engaged in a battle in Najaf on Monday that killed a woman.
Al-Sadr aides have accused police of targeting members of his Mahdi Army.
In other recent developments:
Najaf Gov. Adnan al-Zurufi confirmed that a number of policemen were kidnapped; Ahmed al-Shaibany, an al-Sadr spokesman, denied any police were locked up in al-Sadr's office or any of his quarters.
The deadliest insurgent attack Tuesday came in a car bombing north of the city of Baqoubah, when a truck raced toward an Iraqi checkpoint guarding Kharnabad Bridge, officials said.
The truck attempted to merge into a U.S. military convoy heading toward the bridge, but a soldier driving one of the vehicles forced it off the road before it detonated, said Maj. Neal O'Brien, a U.S. Army spokesman. No U.S. troops were injured, he said.
The blast killed six members of the Iraqi National Guard and wounded six others, said Lt. Mohammed al-Duleimi, of the national guard.
"A U.S. convoy drove past us and just afterward there was an explosion," Cpl. Motaz Abood, whose back, arms and face were covered in burns, said from his hospital bed.
A car bombing Wednesday outside a police station in Baqouba, 35 miles northeast of Baghdad, killed at least 70 people and injured scores more.
The U.S. military reported that two U.S. Marines with the 1st Marine Expeditionary Force were killed in fighting Monday in Anbar province, a volatile, Sunni-dominated region west of Baghdad.
One Marine was killed Monday, the other died Tuesday of wounds, the military said. A third Marine was killed Tuesday after suffering a non-hostile gunshot wound, the military said.
A roadside bomb in Baghdad killed two U.S. soldiers and wounded two others late Monday, the military said. A third soldier was killed Tuesday in a vehicle accident in Baghdad, the military said.
In other violence, a roadside bomb attack early Tuesday killed Col. Mouyad Mohammed Bashar, chief of al-Mamoun police station in Baghdad, along with another officer, officials said. A third officer was wounded in the blast.
Gunmen in the northern city of Mosul opened fire on a police station, killing one officer and injuring two others before fleeing, police chief Izzat Ibrahim said.
From April 2003 to May 2004 alone, 710 Iraqi police were killed out of a total force of 130,000 officers, authorities said.
The pipeline attack came when saboteurs exploded a bomb Tuesday alongside a pipeline that sends oil to Iraq's Beiji refinery as well as to Turkish port of Ceyhan, the main export line from Iraq's northern oil fields. The Ceyhan pipeline already has been idle for weeks due to constant attacks.
Huge plumes of black smoke billowed into the air from the raging fire on the pipeline near al-Fattah, about 135 miles north of Baghdad. The fire blazed all day and fire fighters left it still burning in the evening, witnesses said.
Iraq usually exports about 250,000 barrels of oil a day through Turkey from its northern oil fields. The bulk of Iraq's oil exports, roughly 90 percent, flow from its southern fields.