Thirty-seven civilians were killed and more than 60 wounded when gunmen ambushed a convoy transporting workers of Canadian gold miner Semafo in eastern Burkina Faso, regional authorities said on Wednesday.

The attack is the deadliest in recent years as the military struggles to contain violence that has overrun parts of Burkina Faso, located in West Africa. Semafo tightened security last year following armed incidents near two of its mines in the country.

Semafo said in a statement earlier that the attack on a convoy of five buses with military escort took place on the road to its Boungou mine in the eastern region of Est, about 40km (25 miles) from Boungou, and that there were several fatalities and injuries.

The Est governor's office later gave more details, saying "unidentified armed men laid an ambush for a convoy transporting Semafo workers", giving a provisional civilian death toll of 37 with over 60 wounded.

That toll does not include an unknown number of the security forces who may have been killed in the attack. The toll was likely to rise as there are a large number of people still unaccounted for, according to a security source. 

Two security sources said the military vehicle leading the convoy was struck by an IED on a stretch of road where there is no cellphone network.

Shortly after the initial explosion, an unknown number of gunmen opened fire. One of the sources said it appeared that they targeted the buses as well as the military escort, which was unusual.

Al Jazeera