Fifteen Iranian and three Iraqi gas pipeline workers have been shot dead by gunmen north-east of Baghdad.
The attackers sped up in three cars before opening fire on the workers as they dug a trench to extend the pipeline near the city of Baquba.
Another five Iranians and two Iraqis were wounded in the attack.
At least 17 people were killed in separate attacks elsewhere in Iraq on Friday and 22 terrorism suspects escaped from detention.
The gas pipeline workers were digging a trench to extend the line, intended to connect Iraq's gas network to supplies from neighbouring Iran.
A worker injured in the attack told Reuters that the gunmen approached them in three cars.
"Three of them got out of a car and started firing on the workers inside and outside the trench," Ibrahem Aziz said by phone from hospital.
Security sources told the BBC that the attack happened in a predominantly Sunni area near the city of Baquba, some 50km (30 miles) north of Baghdad.
In other violence:
- Separate car bombs in the southern suburbs of Baghdad killed four in Nahrwan and six in Madain
- Two government employees were killed in a drive-by shooting in western Baghdad
- Five policemen were killed in a car bomb attack on a security checkpoint in the western city of Ramadi
Meanwhile, in Baghdad itself, at least 22 people detained for "issues related to terrorism" escaped on Friday after seizing weapons from their guards.
The interior ministry said one of the detainees was killed and all but three others were later captured, though other reports suggested around eight suspects remained at large. Two guards were reportedly killed.
Violence in Iraq this year has reached a level not seen since 2008.
The UN has said the monthly death toll dropped to 659 in November, including 565 civilians and 94 members of the Iraqi security forces, compared with 979 in October.
But more than 7,150 civilians and 950 security forces personnel have now been killed since January, the highest annual toll since 2008.
Reproduced under licence from BBC News © 2013 BBC