The petrol sold on the black market in Maradi comes from Nigeria
(Representative image) AFP

Gunmen have freed five sisters abducted six months ago from their boarding school in northwest Nigeria after their parents paid ransom money to secure their release, police and relatives said.

The bandits kidnapped 11 schoolgirls, including the sisters, from a secondary school in Zamfara state in March and later released six of them. The sisters were detained because the kidnappers found out their father had previously worked as a senior government official in the state.

Kidnapping has become endemic as roving gangs of armed men abduct people from schools, hospitals, roads and farms and demand ransom money from their relatives.

Hadiza Abubakar, the mother of the school girls, said a total of 72 million naira ($164,000) was paid as ransom in three instalments in exchange for their freedom.

She said the bandits last month posted a video showing her daughters with rifles and ammunitions, pressuring the family to meet their demands.

"Initially, we almost lost hope especially when we saw them in a video with guns around their necks," Abubakar told Reuters.

A Zamfara police spokesperson confirmed the release of the five girls but did not mention the ransom payment.

Last week, a group of 21 children who were abducted by gunmen from a farm in northwestern Nigeria's Katsina state were freed and reunited with their families, police said.

($1 = 439.53 naira)

(Writing by Chijioke Ohuocha; Editing by James Macharia Chege and Hugh Lawson)