LAGOS, Nigeria — Abubakar Shekau said Thursday he is still the leader of Boko Haram, rejecting a successor announced hours earlier by the Islamic State and exposing the biggest rift yet among Nigeria’s deadly Islamic insurgents.

Shekau’s declaration could pave the way for a break from the Islamic State and Boko Haram’s possible return to the influence of Al Qaeda. It also could cause insurgent rivals to turn their guns on each other.

The Islamic State announced Wednesday that Abu Musab al-Barnawi is the new leader of its West Africa province.

But an audio speech purporting to be from Shekau criticized Barnawi and said ISIS leader Abu Bakr al-Baghdadi did not respond to several letters from Shekau explaining that Barnawi is ‘‘an infidel’’ preaching ‘‘false creeds.’’

Shekau called Wednesday’s announcement ‘‘a coup.’’

‘‘Today, I woke up to see one who is an infidel whom they want me to follow. No, I won’t. . . . We cannot subject ourselves to people who are in ignorance of all holy books and teachings,’’ Shekau said in the speech, delivered in Arabic and Hausa and posted on social media.

He also highlighted ideological differences with Barnawi, who promised in an interview published Wednesday in Islamic State newspaper al-Nabaa to end attacks on mosques and markets frequented by Muslims.

Such attacks have been a hallmark of Boko Haram under Shekau, who has led the group since its resurgence as a much more deadly and brutal force in 2009. Under his leadership, the seven-year insurgency spread to neighboring countries, killed more than 20,000 people, and drove more than 2.2 millon from their homes.

In March 2015, Shekau pledged allegiance to Baghdadi.

Shekau in his latest speech still calls Baghdadi his ‘‘caliph,’’ and he accuses his enemies of ‘‘deceit and treachery’’ that have poisoned his relationship with the ISIS leader.

Associated Press