MAIDUGURI, Nigeria, Dec 24 (Reuters) - An explosion tore through a mosque during evening prayers on Wednesday in Maiduguri, the capital of Nigeria’s Borno state, a Reuters witness said. There was no immediate word on casualties or official comment.

The blast occurred in a city that has been at the heart of an Islamist insurgency waged by Boko Haram and its offshoot Islamic State West Africa Province (ISWAP) for nearly two decades which has killed tens of thousands and displaced millions across the northeast.

No group has claimed responsibility, but militants have previously targeted mosques and crowded places in Maiduguri in suicide bombings and improvised explosive device attacks.

Boko Haram launched its uprising in Borno state in 2009, seeking to establish an Islamic caliphate. Despite military offensives and regional cooperation, sporadic attacks continue to threaten civilians in the northeast.