A soldier of the French Army patrols a rural area during the Barkhane operation in northern Burkina Faso, on November 09, 2019. AFP
The ambush took place on Friday in Oudalan province near the restive frontier with Mali and Burkina Faso.
By the end of Monday, "43 new bodies had been found, bringing the provisional death toll to 51 soldiers", the army said in a statement.
Those fatalities were added to an earlier toll of eight soldiers, given by the army on Monday morning.
"Operations are continuing with an intensification of air actions that have made it possible to neutralise around 100 terrorists and destroy their equipment," the military added.
"This figure is in addition to the 60 or so terrorists neutralised since the beginning of the response," it added.
Burkina Faso is battling a jihadist insurgency that spread from neighbouring Mali in 2015.
The violence has led to more than 10,000 deaths, according to estimates by NGOs, and displaced some two million people.
Anger within the military at failures to stem the bloodshed led to two coups last year.
Attacks have mounted since the start of the year, claiming more than 100 lives in the last two weeks, according to an AFP count.
In its statement on Monday, the army called on the Burkinabe population "to unite around the defence and security forces in these difficult times".
In Friday's incident, a military patrol was the victim of a "complex" attack between Deou and Oursi in the Sahel region, bordering Mali and Niger.
"Intense fighting" ensued between members of the military unit that had been attacked and "an armed terrorist group," the army said.
Burkina Faso is one of the world's poorest nations and currently around 40 percent of the West African nation lies outside government control.
Last month its former colonial ruler France confirmed it would withdraw hundreds of troops stationed in Burkina Faso, after the junta ruling the Sahel country demanded the force's pull out within four weeks.
The request came days after Burkina's Prime Minister Apollinaire Kyelem de Tembela declared Russia to be a "reasonable" choice of new partner in the anti-jihadist fight.