Kano - Nigeria's military campaign against Boko Haram Islamists is increasingly bogged down as it confronts suicide attacks, looting and indiscriminate slaughter while the UN warns the affected region faces the "largest crisis in Africa".In northern Borno state, the epicentre of the insurgency that has spread to three neighbouring countries - Chad, Cameroon and Niger - Nigeria's army has unleashed a barrage of air and land assaults.The counter-insurgency has clawed back some territory, but Boko Haram has responded by stepping up guerrilla tactics, ambushing troops when it can and terrorising civilians when it cannot.In late November major general Leo Irbor hailed his men's success in freeing "more than 5 200 people" over a month.But the high number freed merely highlighted Boko Haram's capacity to capture and hold vast, heavily populated areas.Villagers under siege are typically forced to abandon their crops, devastating local food supplies. Those who are freed by the army are generally transported to camps where basic supplies are also desperately scarce.The United Nations estimates that 14 million people will need outside help in 2017, particularly in Borno State, after seven years of conflict that has killed at least 20,000 people and left 2.6 million homeless.'Scorched-earth'The scale of humanitarian suffering has become more apparent as troops recapture and discover the "scorched-earth" conditions of villages that have fallen into the hands of Boko Haram.But local people complain that there are not enough security forces deployed to effectively battle the menace of Boko Haram.The same day as Irbor hailed the liberation of the civilians, five people were killed in insurgent raids on villages near Chibok, the district that gained notoriety for the Boko Haram kidnapping of more than 200 schoolgirls in 2014.The Boko Haram raiders looted and burned houses, set fire to crops that were ready for harvesting, and killed the locals - even though the army had been alerted to the assault."We've heard there are 700 soldiers to secure the zone bordering the Sambisa forest that is the Boko Haram stronghold", said Ayuba Alamson, a resident of Chibok.The forest covers an area of about 1 300 square kilometres."We need another battalion," said Alamson. Though Boko Haram has been weakened and casualty numbers followings its attacks are often low, the frequency of their strikes "enable it to keep up the pressure on security forces and force them to deploy", said Omar Mahmood, a researcher at the Institute for Security Studies, stretching them further. 'Famine-like'Troop numbers are also being pulled away to fight on another front, Nigeria's south where militants have been sabotaging oil pipelines and other installations vital to the country's export earnings in a fierce dispute over local autonomy and the distribution of petrodollars.And with tensions mounting between Shiite and Sunni Muslim communities in the country's northwest, authorities are struggling to guarantee security for Nigeria's 180 million people. The number of killings in the northeast, which increases after the end of the rainy season each year, is a particular cause for concern - especially on the border with Niger.Territory in Niger has become the stronghold of Abu Musab al-Barnawi, who was declared a local leader by the Islamic State group after Boko Haram declared its allegiance to the jihadists. Anti-terrorist consultant Yan St-Pierre, director of the Modern Security Consulting Group, said that pressure on Islamic State jihadists in northern Libya has, perversely, pushed its activities further south, to countries bordering Nigeria.As a result, their "effectiveness for supplying (Nigerian jihadists) with weapons and logistic materiel has greatly improved over several weeks," he told AFP.While IS and Boko Haram fighters battle the Nigerian army, hunger is spreading among both villagers and the swelling ranks of displaced people in the ravaged northeast.The UN has warned that 75 000 children in the region are at risk of death within "a few months".What the World Food Programme has called "famine-like" conditions have prompted experts to warn against seeking victory over the jihadists at all costs."The Nigerian army, which has adopted a purely military strategy for seven years, needs to change its approach if it wants to win this war," said St-Pierre.