A foreign ministry statement quoted by the Anatolia news agency, said eight guards had crossed Turkey's border with Iraq at Habur in four cars, and were on their way to the embassy in Baghdad, when they were attacked around the flashpoint Iraqi city of Mosul.
Five of the security guards along with two Iraqi drivers were killed. Two survivors reached Baghdad, while a third returned to the border at Habur, the statement said.
"Armed men made the passengers get out of the cars, lie on the ground, machine-gunned them and cut off the head off one of them," Muhammet Tahir, an official of the Turkmen Front in Mosul, was quoted as telling the Turkish press agency DHA.
It said US forces who controlled the region had killed two of the attackers.
The CNN-Turk website said one of the victims was a police inspector while three were police officers. About 70 Turkish nationals, mainly truck drivers, have so far been killed in Iraq since the US-led invasion last year, most of them in road violence and several at the hands of hostage-takers.
In Mosul Lieutenant Colonel Paul Hastings, spokesman for Task Force Olympia, said that at 6:00pm Friday, "soldiers of the multinational force went to a crossroads at Yarmuk and discovered three male bodies evidently killed earlier during the day in a rebel attack."
Attackers detonated a bomb near a US military patrol in Mosul on Saturday but missed the patrol and hit a school bus, killing one teenage student and wounding six others, the US military said.
The bomb exploded as the patrol was travelling through an eastern district of the city, closely followed by a minibus carrying students to a nearby high school.
"The blast hit an Iraqi school bus killing one and injuring six, all eighth graders," the military said in a statement. A photographer for Reuters saw several badly wounded teenagers being treated at a local hospital for blast wounds.
No US soldiers were wounded in the attack, but one of the assailants was killed, the statement said.
Gunmen killed the daughter and son-in-law of former Iraqi president Abdel Salam Aref and abducted his 20-year-old grandson Rafel from their Baghdad home, police said Saturday.
The attack happened on Monday evening in the city's western Dakhliya neighbourhood, an officer told AFP, asking not to be named.
The assailants left a statement proclaiming: "This is the fate reserved for traitors."
Aref was head of state from 1963 to his death in 1966. He was succeeded by his brother Abdel Rahman, who was overthrown by Saddam Hussein's Baath party two years later. Aref's daughter Sanaa worked as a teacher while her husband was a doctor.
Iraq's key oil infrastructure suffered five attacks in 24 hours after a voice identified as al-Qaeda leader Osama bin Laden ordered followers to sabotage the West's key oil supplies.
An oil ministry spokesman condemned the upsurge in "terrorist acts" which he said were depriving Iraqis of essential fuel and the country of desperately needed export revenues. There were two blasts on pipelines Saturday and three late Friday, all of them in restive Sunni Arab areas around the capital or in north-central Iraq, officials said.
In the first of Saturday's attacks, saboteurs blew up a section of the pipeline feeding oil from the northern Kirkuk fields to the distribution hub of Baiji, an oil facilities protection officer told AFP.
The section near Fatha, 85 kilometres (just over 50 miles) west of the oil city of Kirkuk, had already been hit on Friday, virtually eliminating its flow.
An hour later, at around 8:30 am (0530 GMT), a second blast hit the pipeline linking Baiji with Baghdad's Daura refinery, network director Majid Mamnum said.
The section breached was at Dijla, 20 kilometres (12 miles) north of the insurgent stronghold of Samarra, Mamnum said.
On Friday evening, saboteurs hit another pipeline supplying crude from the southern Basra fields to the Daura refinery, oil ministry spokesman Jihad Assem said.