Three suicide bombers killed four people and injured eight others in a village near the northeast Nigerian city of Maiduguri, a police spokesman said on Sunday.

A man and two women blew themselves up when they were challenged by a member of the Civilian JTF, a government-approved militia group, just outside Maiduguri, the city worst hit by jihadist group Boko Haram’s eight-year insurgency.

The blasts, in the village of Umariri around 7 kilometers (4 miles) from the city, occurred on Saturday around 9 p.m. (2000 GMT), said Maiduguri police spokesman Victor Isuku.

“Four people which include a Civilian JTF, a woman and her two children died while eight others sustained injuries,” he said.

It is the latest in a string of attacks in the last few days to bear the hallmarks of Boko Haram, which has killed around 15,000 people and forced more than 2 million people to flee their homes in Africa’s most populous nation since 2009.

A man claiming to be the group’s leader appeared in a video circulated on Friday in which he claimed responsibility for bombings in Maiduguri and a raid on the nearby town of Magumeri last week. He also denied that 5,000 hostages held by the group had been freed.

Boko Haram, whose attacks have increased since the end of the rainy season in late 2016, wants to create a state adhering to a strict interpretation of Islamic laws in northeast Nigeria. It also carries out cross-border attacks in neighboring Cameroon, Chad and Niger.