Nigerian authorities say the Boko Haram militant group kidnapped 100 people, and most were freed by security forces from neighbouring Chad.

A Nigerian security official said the abductions took place on Aug. 10 in Doron Baga in the Kukawa local government area, near the border with Chad.

He said Chadian security forces intercepted the group, killed many of the fighters and freed most of those abducted. He spoke on condition of anonymity because he was not authorized to speak to the media.

Muhammed Gava, a member of the anti-Boko Haram vigilante movement, said 20 females and about 70 young men were forced to board speed boats in Lake Chad, which lies on the border between Nigeria, Niger, Cameroon and Chad.

Boko Haram, seen as the number one security threat to Africa's top economy and oil producer, has dramatically increased attacks on civilians in the past year, and the once-grassroots movement has rapidly lost popular support as it gets more bloodthirsty.

Its solution — kidnapping boys and forcing them to fight and abducting girls as sex slaves — is a chilling echo of Ugandan rebel Joseph Kony's Lord's Resistance Army, which has operated in the same way in Uganda, South Sudan and central Africa for decades.

Earlier this year, the militant group kidnapped 300 girls from schools in northern Nigeria, prompting outrage around the world. Several dozen of the girls later managed to escape their captors.

Last month, Boko Haram killed several hundred people when it took control of three villages in the northeastern state of Borno. The militant group is believed to also have been behind a deadly explosion at a mall in Abuja that killed 22 people.