YOLA, Nigeria — Three women suicide bombers, including two carrying babies on their backs, detonated explosions Friday at a checkpoint Nigeria’s northeastern town of Madagali where people were being searched before entering a bustling weekly market, witnesses and an official said.

The blasts killed the women, the babies and two self-defense fighters who wanted to search the bombers, they said.

The fighters’ challenge likely saved many lives. In December, two women suicide bombers killed 57 people and wounded 177, including 120 children, at the Madagali market. Last week, three girl suicide bombers were killed on the outskirts of the same town.

Residents blamed Boko Haram Islamic extremists for the attacks. Madagali is 150 kilometers (90 miles) southeast of Maiduguri, the largest city in northeast Nigeria and the birthplace of Boko Haram’s insurgency.

“They blew up themselves after they were intercepted by local vigilantes stationed at the checkpoint at the entry to town,” resident David Abawu said by telephone. “Two vigilantes lost their lives in the process.”

Two of the bombers had babies strapped to their backs who also died, Adamawa state spokesman Ahmed Sajo told The Associated Press.

Nigeria’s military and civilian self-defense fighters who work with them have intercepted many suicide bombers in recent months.

Boko Haram has used dozens of female suicide bombers, including girls as young as 7, raising questions about whether some of them are coming from their thousands of kidnap victims. A Nigerian army bomb disposal expert also has said some explosives carried by suicide bombers are being detonated remotely, indicating the carriers may not be acting of their free will.

President Muhammadu Buhari declared last month that Boko Haram had been crushed, but it is unlikely there will be a swift end to the suicide bombings and attacks on remote villages and army outposts.

Boko Haram’s seven-year uprising has killed more than 20,000 people, driven 2.6 million from their homes and created a massive humanitarian crisis. The U.N. says 5.1 million people in Nigeria are facing starvation.