(CNN) -- A trucker for the U.N. World Food Program and his assistant were shot and killed earlier this week in southern Sudan while they were delivering food, the agency said on Thursday.
Assailants on Monday shot and killed Hamid Dafaalla, 47, and his assistant. Dafaala worked as a contract trucker for the agency.
"We are shocked and saddened by this heartless killing," said Ebenezer Tagoe, WFP Sudan deputy director.
"We have met representatives of the government of southern Sudan and they have promised a full investigation," Tagoe said.
The incident happened near Mayom, not far from where two World Food Program-contracted drivers were stabbed to death last month.
Another WFP-contracted driver was killed two days later in the volatile Sudanese region of Darfur.