"This is very difficult. My thoughts go out to the relatives and colleagues of those affected," the organization's Secretary-General, Raymond Johansen, told NRK.
Four more deminers were injured. The victims are Ukrainian citizens who worked for Norwegian People's Aid, authorities in the Kherson region told the AFP news agency.
The Norwegian organization has over 450 employees in Ukraine.
Norway's Minister for Development Cooperation Åsmund Aukrust condemns the attack as "completely unacceptable," according to NRK.
Last year, two people were killed in a Russian missile attack on a Danish mine-clearance operation in the Ukrainian city of Chernihiv.
