Five suicide bombers trying to infiltrate Nigeria's northeastern city of Maiduguri have died in explosions that killed at least three civilians, police said Monday, blaming Boko Haram Islamic extremists.

Sunday night's blasts occurred more than 10 kilometers (6 miles) apart on the city's eastern outskirts, deputy superintendent Victor Isuku said.

Three men strapped into explosive vests and firing assault rifles approached a military checkpoint at about 8:20 p.m., he said. One exploded, killing all three and a civilian self-defense fighter. Two hours later, two female bombers blew up, killing themselves and two unidentified people.

Soldiers and civilians fighting alongside them have stopped many suicide bombers before they can reach heavily populated targets in recent months.

The suicide bombings and attacks on remote military outposts and villages continue despite President Muhammadu Buhari's announcement last month that Boko Haram has been crushed since the military destroyed their last Sambisa Forest stronghold.

Boko Haram's seven-year Islamic uprising has killed more than 20,000 people, driven 2.6 million from their homes and created a massive humanitarian crisis in which the United Nations says more than 5 million people face starvation.

AP