BAGHDAD, Iraq -- A suicide bomber dressed as a policeman blew himself up during roll call at the heavily guarded headquarters of an elite commando unit Saturday as attacks in and around Baghdad killed at least 23 people.
Interior Minister Bayan Jabr, meanwhile, said an Iraqi-led offensive to weed out militants in the capital had led to 1,318 arrests and reduced the number of car bomb attacks from an average of 12 a day to less than two.
Two U.S. Marines were killed Friday in a roadside bomb attack near the volatile Anbar province town of Saqlawiyah, west of Fallujah, the military said Saturday. At least 1,693 U.S. military members have died since the Iraq war began in March 2003, according to an Associated Press count.
The attack at the two-story Baghdad headquarters of the Wolf Brigade followed weeks of accusations against the Shiite Muslim-dominated force by Sunni Arab leaders, who accuse it of kidnapping and killing Sunnis, including clerics.
Jabr said the attacker was a former Wolf Brigade member who was targeting the commando force's commander, Brig. Mohammed al-Quraishi.
Three people were killed in the blast, Jabr said, adding that police were searching for two of the suspect's former colleagues. A witness, Maj. Falah al-Mahamdawi, said five people were killed and seven wounded. The discrepancy could not immediately be reconciled.
Gunmen also opened fire on a minibus in Diyara, 30 miles south of Baghdad in the so-called Triangle of Death, killing at least 11 Iraqi construction workers employed at government and U.S. bases, police said.
In Baghdad, gunmen in a speeding car attacked an Interior Ministry commando convoy in western Baghdad's Mansour area, killing three Iraqi forces, police said.
Another suicide car bomber blew himself up Saturday in front of the Slovakian Embassy in southeast Baghdad, injuring four people, according to Iraqi and Slovak officials. Slovakia has 109 soldiers in Iraq mostly for de-mining efforts.
It was unclear how the attacker managed to enter the tightly guarded compound in eastern Baghdad's Bab Sharqi neighborhood with his explosives undetected.
, but his police uniform may have helped him avoid the stringent checks in place.
People entering the compound, which also houses the 10-story Interior Ministry building, must go through metal detectors and be searched by policemen and dogs.
Al-Mahamdawi said the attacker was disguised as a policeman and detonated explosives during a roll call for new commandos.
"I was inside the headquarters building when the explosion took place," al-Mahamdawi said. "Then I saw five dead bodies lying on the ground plus seven injured people, most of them are policemen."
"There was a group of newly graduated commandos gathered in the yard at the time of the explosion," he added. It was unclear if the bomber was standing among the graduates or was nearby.
It was uncertain what motivated the attack. Such violence is usually associated with the Sunni struggle for a role in the country's political process. Sunnis, who comprise only 15 percent to 20 percent of Iraq's 26 million people but dominated the country under Saddam Hussein, resent the rise to power of the majority Shiite community and the U.S.-allied Kurds.
This is believed to be a major factor in the continuing insurgency in Iraq that has killed at least 934 people since the new Shiite-led government was announced April 28.
Jabr said that more than $6 million had been confiscated and 1,318 people arrested, including eight foreigners -- all Arabs, in the ongoing counterinsurgency campaign dubbed "Operation Lightning," which will enter its third week today.
He said car bombings have dropped from an average of 12 a day to less than two since the operation began on May 29. There have been 26 bombings involving cars since the start of the offensive, according to an Associated Press count.
"Operation Lightning has forced the terrorists to flee outside Baghdad," Jabr said at a news conference. "Within the coming six months, God willing, we will spread security all over Iraq."
He added that eight people had been arrested in a Friday car bombing outside a Baghdad falafel restaurant that killed 10 people, including two children.
U.S. soldiers shot to death two Iraqis and wounded two others in Baghdad when their car came too close to an American armored patrol, military spokesman Lt. Jamie Davis said.
An American soldier fired a warning shot, but occupants of the Iraqi vehicle shot at the convoy and sparked a gunbattle, Davis said, adding the American soldiers left the scene without stopping but an American patrol returned later and found "multiple AK-47s" inside the vehicle.
Police Maj. Moussa Abdul-Karim said those killed were Iraqi security guards driving to work in northern Baghdad and were mistakenly shot by American soldiers.
In other developments Saturday:
--Two oil ministry employees were shot to death and another man was critically wounded in southern Baghdad.
--A bomb exploded in a cemetery in the southern city of Najaf, killing two Iraqis, including an 8-year-old girl, and wounding three others from the same family as they were visiting the graves of relatives.
--Iraqi police raided an auto mechanic's workshop in a southeastern suburb of Baghdad and captured five men suspected of rigging car bombs.
Associated Press writers Sameer N. Yacoub, Sinan Salaheddin and Qassim Abdul-Zahra contributed to this report in Baghdad.