At least 24 soldiers were killed and others are unaccounted for after gunmen ambushed a convoy in central Mali.
The army said eight survivors had been found following Saturday's attack, about 60 miles (100km) from the border with Mauritania.
No group has admitted carrying out the raid but Islamist militants are active in the area.
Mali has been blighted by instability since 2012 when an Islamist rebellion broke out in the north.
Army officials said about 12 vehicles had been in the convoy and four of them were destroyed in Saturday's ambush.
BBC Africa editor Will Ross says that with reports of soldiers missing, it is possible that the death toll could be higher than the military is admitting.
It is the biggest loss for the military since November last year when more than 50 soldiers died in an attack.
On Saturday two UN peacekeepers were also killed when a logistics convoy was targeted in the north of the country. The UN has 13,000 troops in Mali.
Since 2012, Malian forces have managed, with French help, to regain control of large swathes of territory taken by militants. France has 4,500 troops deployed in the region.
But thousands of lives have been lost as Mali struggles to contain the violence, which has spread to neighbouring Burkina Faso and Niger.
President Ibrahim Boubakar Keita has offered to open dialogue with the jihadists but our correspondent says there seems little hope of that working.