The attack on the drivers occurred Wednesday evening on a highway about 105 miles north of Baghdad in the largely Sunni province of Salaheddin and ended a day in which at least 23 people were killed and 22 injured in shootings and explosions around the country, CNN reported.
An earlier bomb explosion outside a shopping market in a neighborhood in northeastern Baghdad killed four people and wounded 13, police said.
Wednesday morning, an attack on a security checkpoint about 19 miles north of Mosul left seven federal police officials dead and three others wounded.
Three people in an ambulance were wounded as they responded to the scene, Mosul police said.
"We are deeply concerned by these attacks and by the levels of violence in Iraq," White House spokesman Josh Earnest told reporters.
"These attacks are a reminder of the formidable challenges Iraq continues to face on the security front. ...
"The Iraqis are responsible for their own security and their ability to provide for it is evolving. We are consulting closely with the government of Iraq on ways to enhance their efforts and remain deeply committed to support the government of Iraq's efforts to bring greater stability and prosperity to its people."