At least 20 people have been killed in an attack by Boko Haram militants on a Cameroonian village near the Nigerian border, a security source has said.

"Boko Haram militants on Sunday waited until there were a lot of people at the village market in Tourou before opening fire on the crowd," the source, who asked to remain anonymous, told Anadolu Agency.

The death toll included 19 civilians and a policeman, he added. The Nigeria-based militant group has already been blamed for several previous cross-border attacks in Cameroon.

Boko Haram, which means "Western education is forbidden" in Nigeria's local Hausa language, first emerged in the early 2000s preaching against government misrule and corruption.

The group later became violent, however, after the death of its leader in 2009 while in police custody.

In the five years since, the shadowy sect has been blamed for numerous attacks – on places of worship and government institutions – and thousands of deaths.