The bodies of 49 freshly trained Iraqi National Guard recruits, lined up and executed by insurgents, were discovered on a roadside about 75 miles northeast of Baghdad, Iraqi officials said Sunday.

In a separate attack, a member of the State Department's Bureau of Diplomatic Security was killed when a rocket or mortar round landed in a U.S. military base adjoining the Baghdad airport early Sunday morning. Edward J. Seitz, 41, was the assistant regional security officer for the U.S. Embassy.

The massacre of the recruits occurred shortly after sunset Saturday near the army's main training base in Kirkush, said Col. Adnan Abdul-Rahman, a spokesman for the interim Interior Ministry. The recruits had just departed the base aboard three buses to begin a 20-day leave when they were stopped at a checkpoint manned by insurgents dressed as Iraqi police, residents said, according to Abdul-Rahman.

Most of the recruits appeared to have filed off the buses, lined up in four rows and lain down before they were shot. The first 37 bodies were discovered Saturday night. Another 12 were found after daybreak Sunday a short distance away, still inside the minibus where they were killed. Three drivers were among those killed.

"All of them were from the southern provinces," Abdul-Rahman said of the victims. "Most of them had their hands tied behind their back."

No security vehicles accompanied the minibuses, which were unmarked. The guardsmen were dressed in civilian clothes and were unarmed because they were going on leave, the spokesman said. Their bodies were transported to the nearby town of Mandali, a town on a road that hugs the Iranian border leading south and east from Kirkush.

A group led by Abu Musab Zarqawi, a Jordanian-born militant linked to al Qaeda, asserted responsibility for the attack on the guardsmen, whom it called "apostates," according to a statement posted on the Internet.

The attack was unusual for its boldness if not for its target. The men and women who staff Iraq's nascent security forces -- and whom U.S. officials are counting on to take on a greater role from U.S.-led military forces -- have been killed by the hundreds over the last year, in attacks that appear to be increasing in audacity and frequency.

In the hours before the recruits were killed, at least six other attacks on Iraqi security forces were officially recorded:

* An Iraqi police officer was found dead in a field in Baghdad.

* Another police officer was killed when shots were fired into his patrol car as it made a U-turn on a street in the capital.

* The operations chief of the police department in the Kurdish city of Irbil in northern Iraq was assassinated by a pistol shot.

* A car bomb exploded at an Iraqi National Guard checkpoint in Balad, northwest of Baghdad.

* A roadside bomb exploded beside a police patrol in the southern city of Basra.

* In Dawr, a town in north-central Iraq, three vehicles pulled up to the local police station and 30 men swarmed out; they bound the officers inside and carried away every weapon in the station.

Two attacks on security forces were reported after the roadside massacre. An explosives-laden flashlight was tossed at a National Guard checkpoint near Baqubah, wounding three. Three guardsmen and a civilian driver were injured when a roadside bomb went off beside the vehicle in which they were riding to work, the Associated Press reported.

Iraqis reacted to the massacre with expressions of sympathy for the recruits and a variety of possible explanations.

"Those people are serving their country, why are they killed?" said Salman Mohammed, 42, as he waited for a friend in a Baghdad restaurant where they planned to break their Ramadan fast at sunset. "I think that there are foreign countries that want to destroy these forces. I think the Zionists are behind that. They want to make this country collapse . . . to extend their state from the Nile to the Euphrates."

Sabah Hussein, a baker, noted that many people had come away from encounters with guardsmen feeling abused.

"Of course I am against what happened," said Hussein, 51. "It is terrible. But sometimes I think they don't behave well with the people. A few days ago, they came and raided the nearby husseiniya," he said, referring to a Shiite mosque. "They were really impolite with the people. So maybe there are some people who lost their son, friend, brother or any relative because of them, so they ambushed and killed them.

"Or maybe there are some gangs who were paid to kill them for the sake of some other side which we don't know."

Another Baghdad resident said both sides in the encounter -- insurgents and guard recruits -- were probably interested only in a paycheck.

"There are no jobs, and that is why many young men joined these groups," said Ali Saber, 22, a student in the college of arts at Baghdad University. "Not for the sake of jihad or resistance, but to gain money. And the same is with the National Guardsmen. Most of them, if not all, joined the army for the sake of money."

That reality -- widely acknowledged across Iraq -- has apparently played a role in many attacks. A mortar attack on a National Guard base north of Baghdad last week occurred as 550 guardsmen had gathered in formation.

The deputy governor of Diyala province, Aqil Hamid Adili, said the insurgents clearly had help planning Saturday's mass execution.

"There was probably collusion among the soldiers or other groups," he told the satellite news channel al-Arabiya. "Otherwise, the gunmen would not have gotten the information about the soldiers' departure from their training camp and that they were unarmed."

The State Department said that Seitz, the slain diplomatic security special agent, was killed around 5 a.m. when indirect fire hit Camp Victory, the sprawling U.S. base beside the Baghdad International Airport.

"The Department of State and I mourn the loss of one of our own today in Baghdad," Secretary of State Colin L. Powell said during a tour of Asia. "Ed was a brave American, dedicated to his country and to a brighter future for the people of Iraq."

The Bureau of Diplomatic Security is the State Department's security unit. Its agents conduct a variety of tasks, including designing physical security for U.S. diplomatic buildings and personnel, and assessing threats, investigating attacks and devising responses.

Seitz, who was married, joined the State Department 16 years ago and had been posted to Washington, Chicago and China. He spent four years in Detroit as an investigator with the FBI's joint terrorism task force before heading to Iraq this past summer, according to Terry Booth, an FBI special agent in Detroit.

"He was considered part of our extended family," Booth said. "He was an outgoing and personable guy. Today is a very sad day around our office."

In 1999, Seitz was honored by the State Department for his response to the bombing of the U.S. Embassy in Nairobi. Before joining the State Department, Seitz was a police officer in Cleveland.

In other incidents, a Bulgarian soldier was killed when a car bomb exploded near his convoy in Karbala, about 60 miles southwest of Baghdad. A Turkish truck driver was found shot to death beside a highway near Baiji, north of Baghdad. The headless body of a man was fished out of a river in the northern city of Kirkuk.

A 17-year-old Iraqi girl and an 11-year-old boy were killed and four people wounded in clashes Saturday night between U.S. troops and insurgents on the outskirts of Samarra, 65 miles north of Baghdad, police said on Sunday. Witnesses said a U.S. military Humvee was also damaged, the Reuters news agency reported.

In Fallujah, a U.S. warplane bombed a fortification that insurgents were attempting to rebuild, the military reported.

[In Baghdad, a suspected car bomb exploded near the Australian Embassy Monday morning. The target appeared to be a security convoy; witnesses saw an armored vehicle blown off the road and ambluances tended to an unknown number of wounded and dead.]

Special correspondents Bassam Sebti and Omar Fekeiki in Baghdad and Saad Sarhan in Najaf, and staff writer Anne Hull in Washington contributed to this report.

Members of the Iraqi National Guard stand over the bodies of fellow guardsmen, found on a roadside north of Baghdad. The recent recruits apparently were killed by insurgents who ambushed the buses taking them from their training base to begin a 20-day leave.