"My country will do everything possible to find out who is behind this vile murder," the DRC Foreign Affairs Minister Marie Tumba Nzeza said.
"On behalf of my government, I offer condolences for this immense loss," she added.
The United Nations Organization Stabilization Mission in the Democratic Republic of the Congo (MONUSCO) reported that the attack, in which the driver and a policeman were also killed, was committed against two World Food Program (WFP) vehicles.
The incident took place in Kibumba, North Kivu province, in a natural park located in an area where several irregular armed groups are operating near the border between the DRC, Rwanda, and Uganda.
"There was an exchange of fire between rangers and these attackers. The inhabitants alerted the Army, which came to reinforce the rangers against these militiamen," said Carly Nzanzu Kasivita, the governor of North Kivu province.
Since September 2017, Attanasio had been the head of mission in Kinshasa, where he was carrying out numerous humanitarian projects.