Two Malian humanitarian workers employed by the Norwegian Refugee Council (NRC) were killed when their vehicle struck an improvised explosive device near the city of Timbuktu in northern Mali, the aid agency and the United Nations said.
The incident occurred west of Timbuktu on the road to the town of Goundam at around 4 PM on Thursday.
"This is a tragic loss for the entire international NRC family. My thoughts are with the family and friends of our two colleagues," Jan Egeland, head of the humanitarian agency, said in a statement on Friday.
The NRC said it did not believe the organisation had been specifically targeted in the blast. There was no immediate claim of responsibility.
Al Qaeda-linked Islamists who seized northern Mali in 2012 have carried out a series of insurgent-style attacks since they were scattered across the Sahara by a French-led offensive last year.
Last week, Tuareg separatists beat back Malian government forces in Kidal - another northern town.
David Gressly, the U.N.'s humanitarian action coordinator in Mali, called upon all groups involved in the conflict in the north to protect civilians and allow access to humanitarian organisations.
"It's shocking that humanitarian workers lose their lives when they are attempting to come to the aid of the most vulnerable people," he said.