MAIDUGURI, Nigeria (AP) — Nigerian police confirm that three suicide bombers blew themselves up attempting to get into the northeastern city of Maiduguri.

Police spokesman Victor Isuku said that on Sunday morning two men detonated explosive vests when security agents challenged them near an entry to Maiduguri, the northeastern city that has sustained several attacks. He said the bombers killed only themselves.

Isuku said a lone bomber at a different location also blew himself up, injuring a civilian.

Dozens have died recently in such attacks blamed on Boko Haram Islamic extremists, but many other bombers have been stopped by soldiers and civilian self-defense militia.

Boko Haram has maintained a campaign of suicide bombings since a multinational army forced the extremists out of urban centers.

Some 20,000 people have died in Nigeria's 7-year Islamic uprising.