Following an operation that saw the arrest of a high-profile leader of the militant group Boko Haram Sunday, Nigerian forces have said they uncovered large quantities of explosives and weaponry. Nine terrorists had reportedly snuck into Maiduguri, a city that has been the site of countless insurgent attacks, armed with AK-47 assault rifles and a vehicle with some 20 improvised explosive devices, the country's Defense Headquarters said online Monday.  

Security forces encouraged police forces and the public to remain vigilant and security conscious, particularly in places that have regularly been targeted by insurgents, like places of worship, markets and schools, the Daily Post reported. Gas cylinders, welding machines, pipes and poles, as well as rocket shells, large quantities of chemicals and other laboratory equipment were also discovered.

Boko Haram has waged a brutal insurgency for the last six years in Nigeria's northeast region in hopes of driving out the central government and establishing an Islamic state in its place. The country has seen upward of 15,000 deaths as a result between government and insurgent fighting since Boko Haram fighters turned violent in 2009. 

Nigerian President Muhammadu Buhari was elected earlier this year in a campaign that focused primarily on security. After being sworn in as the country's leader, he tasked new military chiefs in August with ending the bloody conflict within three months. So far the insurgency has persisted, but under his leadership, Boko Haram has faced setbacks. They have been driven out of dozens of towns, and in response, have stepped up attacks on population centers.

John Trankil, arrested Monday, has been labeled a "kingpin" of the insurgent group by Nigerian news outlets. His arrest came just days after the several other high-profile leaders were reportedly arrested.

The militant group pledged allegiance to the Islamic State group, also known as ISIS, in March. The same month, Boko Haram released an ISIS-style beheading video of two individuals accused of spying.