KANO, Nigeria (AFP) - Boko Haram leader Abubakar Shekau vowed in a new video released on Monday that the group would defeat a regional force fighting the militants in Nigeria's far northeast, Niger and Cameroon.

"Your alliance will not achieve anything. Amass all your weapons and face us. We welcome you," he said in a 28-minute speech, one of three videos posted by the group on YouTube.

Troops from Nigeria have been joined by soldiers from Chad, Cameroon and Niger in recent weeks because of increased concerns about Boko Haram's threat to regional security.

The video came as the militant group launched a fresh attack in neighbouring Niger on Monday, raiding a prison in the southeastern border town of Diffa, humanitarian sources said.

The attackers were repelled after a heavy exchange of fire, the sources said. No casualty toll was immediately available.