Nigeria’s President Bola Tinubu has replaced top security officials as the country grapples with unabated violence in the conflict-hit north and myriad security challenges.

No reason was given but the shake-up comes as the government has denied rumours of a coup plot in the wake of local media reports that at least 20 military officers were arrested in September, including a brigadier general and a colonel.

Nigeria’s capital, Abuja, was also shaken by protests this week as police fired tear gas and arrested dozens of protesters who took to the streets to demand the release of Nnamdi Kanu, leader of the Indigenous People of Biafra separatist group that seeks independence for Nigeria’s southeastern region.

A wide spectrum of armed groups operate across the country. The Islamic militant Boko Haram, Nigeria’s homegrown jihadi group, this year mounted a major resurgence. The group took up arms in 2009 to fight Western education and impose its radical version of Islamic law.

Boko Haram’s splinter faction Ansaru and the Islamic State group’s affiliate, known as Islamic State West Africa Province, have also staged attacks. Criminal groups specialising in kidnapping for ransom and looting — commonly referred to as bandits — are also dominant.

In recent months, Islamic extremists have repeatedly overrun military outposts, mined roads with bombs and raided civilian communities, raising fears of a possible return to the peak insecurity of the Boko Haram era despite the military’s claims of success against them.

Earlier this year, the US government approved the sale of $346 million in arms to bolster Nigeria’s fight against insurgency and criminal groups.