An Islamist insurgency that has increasingly targeted churches has sparked fears of wider unrest in Nigeria after anger boiled over at the weekend, resulting in deadly riots by Christian mobs. Christian leaders and others in Africa\'s most populous nation have warned in recent days that the government\'s failure to stop Islamist group Boko Haram could lead to more cases of residents taking the law into their own hands. The potential for further reprisal violence poses unsettling risks for the continent\'s largest oil producer -- a country of some 160 million people, roughly divided between a mainly Muslim north and mostly Christian south. \"We now have a dangerous situation because things are literally in free fall,\" said Matthew Kukah, a Catholic bishop and respected voice among both Christians and Muslims who has served on various national reform committees. \"If the government is failing to deal with the situation in that way, we are becoming increasingly vulnerable.\" Criticism has mounted over the government\'s response to the violence, with few public indications of what strategies are being employed beyond heavy-handed military raids to stop the onslaught of attacks that has killed hundreds. President Goodluck Jonathan\'s comments have often been limited to reassurances that the attacks will soon end. He provoked criticism when he left for a U.N. environmental summit in Rio on Tuesday as more riots broke out. A front page headline on Tuesday in national newspaper The Punch blared: \"Jonathan off to Brazil as Kaduna, Yobe burn.\" Besides the bombings and riots in Kaduna, gun battles also broke out between security forces and suspected Islamists in northeastern Yobe state on Monday and Tuesday. Violence between Sunday and Tuesday in both Kaduna and Yobe left at least 101 people dead. Round-the-clock curfews have been slapped on both areas. Abubakar Tsav, a respected former police chief for the economic capital Lagos who now lives in Kano, the largest city in the north, said he feared more reprisals could lead to chaos. \"Government is not doing anything to protect them,\" said Tsav. \"That\'s why they\'ve started these reprisal attacks, and that can lead to a breakdown of law and order in the country. People have lost hope in the government.\" The country\'s main Christian body this week issued particularly harsh criticism of Jonathan, himself a Christian from the country\'s south, while the PENGASSAN oil workers union evoked the break-up of the former Yugoslavia. While criticism of leaders is by no means new in Nigeria\'s high-volume political scene, the tone and directness of the recent statements have been striking. \"Since these terrorist acts began, nothing the president ... has done has been reassuring that the end to this spate of bombings and gun attacks is in sight,\" the Christian Association of Nigeria said. \"On the contrary, his utterances after each bombing and killings, even if unwittingly, seem to have cast a hallmark of weakness on his presidency and an escalation of the terrorist acts.\" There have regularly been warnings in the past over whether Nigeria\'s divisions could lead to all-out conflict, and the country has repeatedly overcome doomsday predictions. But Boko Haram\'s violence has posed a new kind of threat, with its scores of attacks including suicide bombings of police headquarters, the U.N. building in the capital Abuja and an office for one of the country\'s most prominent newspapers. Muslims have often been its victims, but Boko Haram has recently specifically targeted churches with deadly results, including on Christmas and Easter. Despite that, many observers continue to caution that viewing the unrest as strictly \"religious violence\" is to misunderstand it. A number of analysts say anger and poverty in the deeply impoverished north has been a major factor in creating the insurgency, as has the massive corruption at virtually all levels of society in Nigeria. A drive through the northeastern city of Maiduguri, Boko Haram\'s base, reveals striking contrasts, as is the case throughout the country. Mansions sit behind security walls in upscale neighborhoods while poor residents fetch water from wells and live without electricity elsewhere. \"Frankly, we are just reaping the seeds of what we sowed,\" Bishop Kukah said. \"For me, Boko Haram is a metaphor for everything that is wrong with Nigeria.\" Yet the question of how to address the problem in the short-term remains. Members of Boko Haram are believed to have sought training in northern Mali from Al-Qaida\'s North African branch and Western nations have been monitoring closely for signs of further ties. Many say Nigeria\'s intelligence capabilities must be greatly strengthened, while adding that some form of dialogue will also be needed. Others also criticize Jonathan\'s government for failing to arrest and prosecute more of Boko Haram\'s leaders, though a number of the group\'s alleged members have been killed in recent raids, particularly after kidnappings of foreigners. \"These people are not spirits,\" Tsav said. \"They live with us.\"