Suspected Boko Haram jihadists killed five fishermen on a remote island in northeastern Nigeria for aiding the search for dozens of schoolgirls kidnapped last month by the jihadists, a local official said Saturday.

“Five men who went fishing near the border with Chad were shot dead,” said Abubakar Gamandi, president of the fisheries union in Borno state, where the killings occurred.

He said the attack happened on Tudun Umbrella island in Lake Chad, which borders Nigeria, Chad and Cameroon.

Members of the militant Islamist group stormed the Government Girls Science and Technical College in Dapchi, Yobe state, in February, taking 110 girls with them as they fled.

The Dapchi kidnapping rekindled painful memories of a similar mass abduction by Boko Haram four years ago, when more than 200 schoolgirls were taken from Chibok in an act that shocked the world.

Nigerian President Muhammadu Buhari called the February 19 abduction a “national disaster” and a widespread hunt for the girls is underway.

Gamandi said the fishermen were killed because they were assisting the military in the search.

“Fishermen have been assisting the military in the operation to locate the schoolgirls because we know the terrain well,” he told AFP.

Boko Haram has repeatedly attacked fishermen in the border region around Lake Chad in recent years.

Nigeria’s battle against the extremist group in northeastern regions has left more than 20,000 people dead and forced more than 1.5 million to flee their homes since 2009.