Yaound - At least 16 people were killed in a raid and suicide attack in Cameroon and Nigeria on Monday, in the latest violence blamed on Boko Haram Islamists.A civilian militia member said 11 people had been "slaughtered" overnight Sunday-Monday in the village of Gouderi, in the Kolofata region of Cameroon's Far North."Boko Haram's incursion in Gouderi was an act of revenge," said the militia member, who asked not to be identified for security reasons."The jihadists acted after the arrest in the area of some of their colleagues," he added.Civilians were also the target of a suicide bomber at a mosque in Ajiri Yala, 15km north of the Borno state capital, Maiduguri, in northeast Nigeria.The leader of the local Civilian Joint Task Force (CJTF) helping the military with security said the attack happened at about 04:30 (0330 GMT)."A male suicide bomber disguised as a worshipper entered the mosque while people were gathering for the morning prayers," Modu Bukar told AFP by telephone."He detonated his explosives. He killed five people and injured several others." 'Major concern' The violence followed another attempted suicide attack against civilians and a clash between soldiers and militants at the weekend that saw the jihadists suffer heavy casualties.Nigeria maintains Boko Haram is a spent force but the latest attacks underline the persistent threat posed by the group, whose insurgency has killed at least 20 000 since 2009.Boko Haram typically never claims responsibility but has used suicide bombing as a frequent tactic in its eight-year insurgency to establish a hardline Islamic state.Mosques that do not ascribe to its extremist views are seen as legitimate targets, as are people and places seen to be supportive of the secular government.On Sunday, a CJTF member manning a checkpoint in the Muna area of Maiduguri was killed and another injured when two women strapped with explosives blew themselves up.A day earlier, a military source said, troops inflicted heavy losses on a large contingent of Boko Haram fighters near the Yobe village of Goniri.The previous weekend, 14 people were killed when three women detonated their explosives near the Muna Garage camp, which is home to tens of thousands of people made homeless by the violence.The United Nations warned recently that attack against internally displaced people (IDPs) in camps across the region was "a major concern". Lurking remnants Communities in hard-to-reach areas of the remote region are also vulnerable and at the weekend, two women blew themselves up in the Gulak area of Madagali, in the far north of Adamawa state.A former Madagali local government area chairperson, Maina Ularamu, said there were two blasts in Dar village on Saturday night and Sunday morning."Our suspicion is that they intended to attack the church, which is located inside the primary school about 100 metres away from the scene of the explosion," he said.Ularamu said locals suspected the two women had come to Dar from the Sambisa Forest, in neighbouring Borno, where Boko Haram is known to have bases.The military said earlier this year it had retaken control of the former national park but there are reports the militants have moved back in.They are also known to have been holed up in the Mandara mountains that lie east of Madagali and form the border between Nigeria and Cameroon.On August 2, Boko Haram fighters stormed the village of Mildu, near Madagali, killing six.Ularamu said Boko Haram "remnants are still lurking" in remote villages and the Sambisa Forest, and troop reinforcements were needed.Attacks on civilians have largely been attributed to the Boko Haram faction led by Abubakar Shekau.Strikes against the military are generally blamed on the Islamic State group-supported faction headed by Abu Mus'ab al-Barnawi.