The attack took place at the entrance to the town of Mora in Cameroon's Far North region, about 30 km from the border with Nigeria.
One of the military sources, who requested not to be identified, attributed it to the Islamist Boko Haram, which is waging an insurgency in the region.
He also said that one soldier and two Boko Haram fighters were killed in a separate attack on Monday evening on a military post in the Far North town of Ziguague.
"It is the first time since 2013 that we are having such an attack in our municipality," the mayor of Mora, Chetima Hamidou, told Reuters.
Mora was hit by several suicide bomb attacks in 2015 and 2016 by suspected militants from Boko Haram.