Nigerian President Muhammadu Buhari on Sunday "strongly" condemned recent attacks by cattle raiders on three villages in the country's northwest that officials said killed 37 people.He offered commiserations to the survivors and vowed a firm response to "these brutal and remorseless enemies of humanity"."These frequent and large scale killings of poor villagers by gangs of mass murderers must be met with the fiercest force the government can mobilise," presidential assistant Garba Shehu quoted Buhari as saying. On Wednesday, armed men on motorcycles raided three villages in the district of Goronyo in the Nigerian state of Sokoto, district chief Zakari Chinaka told AFP."The bandits opened fire on the villages and set shops and grain stores ablaze. They took away all the cattle in the villages," he said."They operated for two hours unchallenged (by any security forces) because of the difficulty of the terrain which makes it hard to access," said the chief.Alu Ibrahim, a resident of the village of Kamitau, where 23 people died, said villagers had pursued the bandits in a bid to recover their stolen cattle -- key to survival in the poor, remote region."The bandits turned their guns on them and killed many. This was the reason for the high death toll from Kamitau," said Ibrahim.Criminal gangs of cattle rustlers have increasingly targeted rural communities in Sokoto state.Last month, motorcycle-riding bandits killed 43 people in two days of attacks on five villages in Rabah and Isa districts, according police and locals.Rural communities in the north of Nigeria have for years been terrorised by gangs who raid villages, stealing cattle, kidnapping for ransom and burning homes after looting food supplies.Villagers have taken up arms to defend themselves, but these vigilantes are now accused of extra-judicial killings of suspected bandits.The bandit gangs are one of a string of security challenges facing Nigeria, including attacks from a Islamic State-backed Boko Haram faction and renewed clashes between livestock herders and farmers.This has left the military overstretched and Buhari criticised for failing to protect lives and property, despite promises to boost security.