Nagorno-Karabakh, a mountainous part of Azerbaijan, is run by politicians of Armenian descent. In the territory, a conflict broke out as the Soviet Union crumbled in 1991.

Though a ceasefire was agreed in 1994, Azerbaijan and Armenia still regularly accuse each other of carrying out attacks in the area. The conflict flared up again in 2016 and saw a number of deadly incidents over the past year.

“Our colleagues were killed while working to make the land safe for the people of Nagorno-Karabakh,” The Halo Trust, a Scottish charity that has cleared minefields worldwide and was once sponsored by the late Princess Diana, said in a social media post.

The region’s self-proclaimed foreign ministry confirmed the incident. Authorities said the staff who were killed were locals.