They were lying in ambush. When the Boko Haram militants on board motorbikes saw a group of Christians returning home from church service, they opened fire, killing eight of them, according to survivors.

The incident, which took place in Kwamjilari village in Nigeria, was just one of three attacks launched on Sunday and Monday by the Muslim extremists, the New York Times reports. The two other attacks killed at least 10 people, Nigerian military authorities said

After the attack on Christian churchgoers on Sunday, the Boko Haram militants beheaded a village chief and his son and then set their homes and others on fire before dawn on Monday, the authorities said. The militants then opened fire on fleeing villagers, killing two people and injuring others.

Later on Monday, the Muslim extremists shot and killed six civilians and wounded three soldiers traveling in a convoy, an army spokesman said.

The attacks came following failed negotiations between Boko Haram and the Nigerian government to exchange kidnapped women and girls for imprisoned militants, according to Mission Network News.

The missionary group World Mission notes that Boko Haram militants have been terrorising northern Nigeria for seven years now. Unfortunately, the crisis has not been grabbing headlines in the West, which is focused on the Islamic State (ISIS) atrocities in the Middle East, World Mission CEO Greg Kelley said.

"They're [Boko Haram] causing all kinds of terror and it's incredibly difficult. In fact, there are so many communities in northern Nigeria that Christians have 100 percent evacuated just because they are literally targeted and murdered on site as they're identified," Kelley told Mission Network News.

He said the crisis is not just Nigeria's problem since it affects countries around them.

"The reality is that Boko Haram, although they're concentrated in Nigeria, their influence has spilled over into Niger and Cameroon, specifically where you have hundreds of thousands of refugees. The numbers we have are that there's an additional 400,000 refugees in just those two countries as a result of Boko Haram," Kelley said.

Despite the danger of preaching God's Word in this part of Nigeria, Kelley said World Mission is there to share the gospel, even with the terrorists.

"Literally, as Christians are fleeing, the people we work with are leaning into and going into those very places and sharing the Gospel with these terrorists, essentially," he said.