A former member of one of Iraq's most feared counterterrorism squads walked into the unit's headquarters Saturday and detonated an explosive belt hidden under his police uniform, killing himself and three other people, according to Interior Ministry officials.

South of Baghdad, in the area known as the "triangle of death" because of the frequency of insurgent attacks there, gunmen attacked a minibus full of Iraqi construction workers, killing 10 and wounding four, regional officials said.

And in far western Iraq, U.S. Marines backed by warplanes and attack helicopters battled insurgents on the outskirts of Karabilah.

A Marine spokesman in Ramadi, Capt. Jeffrey S. Pool, said that an estimated 40 insurgents were killed in the fighting and that the Marines suffered no casualties. Pool said the insurgents had set up an illegal checkpoint outside Karabilah, which is situated between Qaim and Habbaniyah, two of the west's most volatile towns.

The suicide bomber -- who was from Latifiyah, 20 miles south of Baghdad, but whose name was not released -- attacked the home of the Wolf Brigade, an Interior Ministry unit that has been at the forefront of counterterrorism efforts. Interior Minister Bayan Jabr, speaking to reporters after the bombing, said the attacker was a former member of the unit and was trying to kill its leader, Gen. Muhammad Quraishi.

"But he failed to reach him and blew himself up in the training field," Jabr said. "The result was three martyrs killed and one wounded, and this is the nature of the battle between good and evil."

Quraishi, popularly known as Abu Walid, is well known in Iraq as the host of a television show on which accused insurgents confess their crimes. Quraishi and the bulk of the Wolf Brigade are Shiite Muslims, and leaders of Iraq's Sunni Muslim minority have accused the brigade of conducting kidnappings and summary executions during an ongoing security crackdown known as Operation Lightning. Quraishi has repeatedly denied the allegations.

Jabr echoed recent statements by Iraqi officials calling Operation Lightning a huge success that has dramatically reduced the number of car bombings and other such attacks in and around Baghdad since it began May 29. During a surge of insurgent attacks in May, "there were about 12 to 14 car bombs exploding in Baghdad per day," Jabr said, pointing to a diagram that tracked the trend. "Now we have one car bomb or two per day."

Jabr said 36 terrorism suspects had been killed in gunfights during the operation and 1,318 had been arrested, including four Sudanese, two Jordanians, an Egyptian, a Syrian and a Palestinian. A total of $6 million was found in the suspects' possession, Jabr said, as well as dozens of rockets, mortars and rifles.

"There is no doubt that Operation Lightning is closing the circle on the terrorists inside Baghdad, which led them to try to escape outside it," Jabr said. "That is why we're prepared for that, and that is why there were operations in Mahmudiyah, Latifiyah and Jurf Sakhar, and we will have similar operations in surrounding areas of Baghdad within the coming few days."

Less than an hour after Jabr's news conference, a suicide bomber struck the Slovak Embassy in southwestern Baghdad. The driver of an explosive-laden vehicle was the only person killed, but four Iraqi guards were wounded, according to embassy officials. Also in Baghdad, U.S. soldiers shot to death two Iraqis and wounded two others when their car came too close to an American armored patrol, the Associated Press reported.

Meanwhile, the death toll in a suicide car bombing Friday night in a Shiite neighborhood in north Baghdad increased to 10 Iraqis, including two children, according to the news service.

Two U.S. Marines also were reported killed. A statement released Saturday by the U.S. military said they died Friday when a roadside bomb exploded near their vehicle in Saqlawiyah, west of Fallujah.

And in the northern city of Mosul, gunmen attacked three trucks belonging to the Iraqi Trade Ministry. The attack killed one driver and wounded two, police Gen. Wathiq Mohammed said.

Special correspondents Saad Sarhan in Najaf and Dhlovan Brwari in Mosul contributed to this report.

A man inspects a minibus that was attacked by gunmen south of Baghdad.