Burkina Faso has been battling jihadists in the north as an Islamist militant insrgency that began in Mali spreads across the Sahel region.

"A vehicle with a military unit from Banh hit an explosive device while on an escort mission," a security source said late Wednesday.

"Four military were killed in this ambush and another three were injured."

Another military vehicle that was reinforcing the first unit also hit an explosive device, leaving five people injured, the security source said.

Jihadist attacks in Burkina Faso, which borders Mali and Niger, have killed around 800 people and forced 800,000 from their homes since 2015.

One of the poorest countries in the world, Burkina Faso's armed forces struggle with poor equipment and lack of training and funding despite being part of a regional Sahel anti-jihadist campaign with neighbouring states.

Militants are increasingly using improvised explosive devices and landmines in Burkina Faso, often combining them with ambushes.

Across the Sahel, Islamist militants -- as well as the intercommunal violence they have provoked -- killed around 4,000 last year in Burkina Faso, Mali and Niger, according to the UN.