A member of the Carabinieri, the national gendarmerie of Italy, identified as Vittorio Iacovacci, and an unnamed driver of one of the vehicles were also killed, according to Italian and U.N. officials.
The Italian Ministry of Foreign Affairs and International Cooperation confirmed the deaths of Attanasio and Iacovacci in a statement, expressing "deep sorrow." The ministry said the pair were traveling in a vehicle that was part of a convoy of the U.N.'s peacekeeping mission in the Democratic Republic of the Congo, known by its French acronym MONUSCO. The deadly attack occurred near Goma, the capital of North Kivu province, which is located in the eastern part of the country near the border with Rwanda.
Italian Foreign Minister Luigi Di Maio said he learned of their deaths "with great dismay and immense sorrow."
"Two servants of the State who were violently snatched from us in the performance of their duty," Maio said in a statement. "The circumstances of this brutal attack are still unclear and no effort will be spared to shed light on what happened."
Italian President Sergio Mattarella condemned the "treacherous act of violence," describing it as a "cowardly attack."
The delegation was traveling from Goma to the eastern town of Rutshuru to visit a school feeding program run by the World Food Program (WFP), the food-assistance branch of the U.N., according to a statement from the organization, which confirmed the death of a "WFP driver." A number of other passengers traveling with the delegation were injured in the attack.
"WFP will work with national authorities to determine the details behind the attack, which occurred on a road that had previously been cleared for travel without security escorts," the organization said. "WFP is in close contact with the Italian authorities through its offices at its Rome headquarters and in the DRC."
A spokesperson for the country's Virunga National Park, which is famous for its endangered mountain gorillas, told ABC News that the attack occurred "on the periphery" of the park but wouldn't provide any further details.
"Virunga National Park is working closely with all relevant parties on this horrific attack," the spokesperson said in a statement.
The eastern Democratic Republic of the Congo is home to numerous rebel groups vying for control over the mineral-rich land. Rangers in the Virunga National Park, which stretches along the country's eastern border with Rwanda and Uganda, are often targeted in attacks. Last month, six rangers who were patrolling the park by foot were killed in an ambush by armed assailants, according to a statement from the Virunga National Park.
The U.N. secretary-general's spokesman, Stephane Dujarric, said Monday's attack was carried out by "unidentified armed elements."
"The Secretary-General calls on the Government of the Democratic Republic of the Congo to investigate swiftly this heinous targeting of a United Nations joint field mission and to bring the perpetrators to justice," Dujarric said in a statement. "He reaffirms that the United Nations will continue to support the Congolese Government and people in their efforts to bring about peace and stability in the east of the country."