Fourteen people were killed and nine wounded in a bomb attack on a bus bringing children back from a school break in northern Burkina Faso on Saturday, two security sources and a police source said.

It was not immediately clear who was responsible for the blast, which occurred in Sourou province near the border with Mali, or how many of the dead were children.

Groups with links to al Qaeda and Islamic State have increased attacks in the area over the past two years despite international efforts to stamp them out.

Insurgents killed 35 mostly female civilians on December 24 after attacking a military outpost in Soum Province, also in the north. About 87 militants and local security forces were killed in the clash, authorities said.

Burkina Faso has lost its reputation as a pocket of relative calm in the Sahel region as a homegrown insurgency has been amplified by a spillover of jihadist violence and crime from its chaotic northern neighbour Mali.

Attacks over the past year have killed hundreds and forced nearly a million people from their homes.