Three migrants died of thirst when their vehicle broke down in the Nigerien desert while en route for Libya, the springboard for migration to Europe, a local official said.
"About 10" other passengers were saved after their vehicle was spotted by the Nigerien army, an official in the northern town of Agadez said.
The group had got lost while searching for one of two wells on their itinerary and their vehicle broke down, the source said.
"All three (fatalities) were Nigerien," the official said.
Death from thirst or heat is a major peril for migrants seeking to cross the Sahara to reach Libya, which lies to the northeast of Niger.
Once in Libya, many try to cross the Mediterranean to southern Europe -- a trip that itself is notoriously risky.
The army and the International Organisation of Migration (IOM) say their desert patrols in Niger have saved thousands of lives over the past two years.
In some cases, the travellers' bus or truck breaks down and in others, they are abandoned by their smugglers.
In the peak year of 2017, 150,000 crossed through the country -- a figure that has fallen to between 5,000 and 10,000, according to a figure cited by German Chancellor Angela Merkel in a visit to Niamey in early May.
One factor behind the fall is application of a 2015 law which sets down jail terms of up to 30 years for traffickers.
One consequence, though, has been that smugglers are likelier to travel at night and on new or little-used roads, heightening the risk of a mishap, say experts.