"We are annoyed to be fighting this war alone," sighs an officer. While the Boko Haram attacks are increasing in Cameroon, people are beginning to denounce the inaction of Nigeria, stronghold of the Islamist group.

"The attacks against our territory come from a neighbouring country (Nigeria) which is not doing anything to help us", denounced head of the Department of Defense on condition of anonymity. For him, the Cameroon leads "a proxy war".

For months in northern Cameroon, the army under pressure attempts to contain the raids of Boko Haram. And the Nigerian group is more content to massacre civilians and launch raids in villages, and they directly attacked the Cameroonian military bases.

"We are all alone at the front", said a commander of the rapid intervention battalion (BIR), a unit of elite formed by Israelis in the first line deal with the Islamists.

On the other side of the border, in northeastern Nigeria, Boko Haram now controls the whole swathes of land deserted by local authorities where locals have been abandoned to their fate.

Thus Amchide, city straddling the two countries, the Cameroonian soldiers are directly facing the enemy, installed across the bridge that materializes the border after having routed the Nigerian Army.

Only a disturbing no-man's-land of dusty and deserted alleys now separates them. "Whenever Boko Haram seizes a Nigerian city, they retrieve all military equipment on-site. So now they have heavy arms," said a source close to the intelligence services.

On several occasions in recent months, Cameroon has even hosted Nigerian soldiers fleeing the rapid progression of the Islamist group in their country.