Fifty-one civilians in northern Mali were massacred and 12 troops were killed in an ambush in neighbouring Burkina Faso, the authorities said on Monday, highlighting the security crisis gripping the two fragile states. “Terrorists” on Sunday invaded the villages of Karou, Ouatagouna and Daoutegeft near Mali's border with Niger, a military officer told AFP. “ (They) massacred everyone,” the source said. A document by the local prefecture, seen by AFP, said 51 people had been killed in the co-ordinated attacks, while homes had been looted and cattle stolen. A local official said: “20 civilians were massacred in Karou, 14 civilians were killed in Ouatagouna, and other civilians were killed in the hamlet of Daoutegeft". The assailants arrived by motorbike, taking the villagers by surprise, he said. An official at a fourth village said his locality had also come under attack. An army unit has been sent to provide help, a military officer said, but a source at a Malian NGO said communications with the remote area were poor as terrorists had attacked telecoms sites. Mali, a landlocked and impoverished state in the heart of West Africa's sub-Sahara region, has been battling a terrorist insurgency since 2012. The crisis began with unrest in the north of the country that spread to Mali's ethnically volatile centre and then to neighbouring Niger and Burkina Faso. Armed groups linked to Al-Qaeda and ISIS are steering the campaign today. Thousands of civilians and troops have died and hundreds of thousands of people have fled their homes. Mali has suffered two coups since August last year, and on July 20 military leader Colonel Assimi Goita survived an attempted assassination at a mosque in Bamako. Alioune Tine, an independent expert on human rights in the sub-Sahara who reports to the United Nations, last week warned that a “critical threshold” had been breached in the country's security situation. At the end of an 11-day visit, he highlighted “the failure of the institutions of state,” as well as “relentless attacks on civilian populations” by terrorists. The armed forces themselves have committed violence against civilians, he said. In Burkina Faso, meanwhile, 12 troops were killed and eight were wounded on Sunday in an ambush near the border with Mali, the government said. “Members of the ground forces and the rapid intervention force GARSI were ambushed” in the north-west Bouclé du Mouhoun region, Communications Minister Ousseni Tamboura said on Monday. The attack occurred near the village of Dounkoun in Toeni district. President Roch Marc Christian Kabore said on Twitter that “we continue to wage without concession the war the obscurantist and barbaric forces have imposed on our country.” A security source told AFP that the ambush had happened at about 3pm GMT, and vehicles had been destroyed or captured. The attack was “revenge for the death of two jihadist leaders who were active in the same Bouclé du Mouhoun region, who were neutralised [on Saturday] by the armed forces,” the source said. He named the two as Sidibe Ousmane, also known as “Mouslim,” and spiritual leader Bande Amadou. A special army unit killed them following exchanges of fire between Diamasso and Bouni, in Kossi province, the government said on Sunday in a statement.